Kieran's eyes gobbled the paradise of sweetness in front of him. Big vats of honey coated sweet popcorn called to him through the Perspex window in the counter, while football [dash] sized jars displayed a billion sweet wonders. In his mind, tangy sherbet itched [not sure if "itched" is an appropriate verb here] at Kieran's lips, rubbery jellied worms slithered across his tongue, and milk chocolate creamyness filled his mouth.
If anyone else would care to comment on any other aspects of this piece that are not quite right, including grammar, I'd be most appreciative.
Well, here's my help:
The Landscape-Cinema complex bustled as Kieran and his school buddy, Mark Johnson, –
[either a comma or a hyphen; you don't need both. Personally I'd opt for the dash, since it's quite an intrusive addition to the normal sentence] known affectionately as Splotch ‘coz
[use "because" instead? Just a personal preference, but I'd try to avoid using contractions (shortened words) in narrative. They're fine in speech, of course, since everyone usually shortens words] his tee shirt was normally covered in food stains of one sort or another – pocketed their movie tickets and headed to the sweet counter.
A big sign, five foot high
[comma. Use a comma to separate off the beginning and end of an additional piece of info that can be removed from the original sentence without altering its meaning; e.g. if you removed the words "five foot high", your sentence is still understandable; therefore, when you write the extra details in, separate them with commas] reached to the top of Kieran’s head. It read, “Remember kids!
[without the comma before "kids" this sentence means "remember the kids and don't forget them!"] Never take sweets from strangers – buy your sweets at Landscape
[in your first paragraph you have a dash here. Be consistent] Cinemas instead, because we’re your friend!”
“What a load of crap that is,” Mark said, looking up at the poster. He was only 11,
[some people would remove this comma. I would too] and hadn’t grown much above four foot five inches yet – even counting the top of his spiky black hair.
“I don’t care if they’re my friend or not,” Kieran replied, “just let me at all those luuuuuvelly
[personal preference, but I prefer leaving the words as normal, i.e. "lovely". If you really have to exaggerate the word and call attention to it, you could always italicise] sweets!” They both laughed at the way he said it.
Kieran’s eyes gobbled
[eyes can't "gobble", so I'm not sure the metaphor fits here. Perhaps "eyes widened at"] the paradise of sweetness in front of him. Big vats of honey coated sweet popcorn called to him through the Perspex window in the counter, but that
[alone] wasn’t enough
[by itself
= remove] to make this a sweet-lovers paradise. On the counter and shelves at the back were football-sized sweet jars tauntingly displaying their sherbetty pink bon-bons, mint-choc chunks, orange sparkles, purple and green wriggly sugared worms and a billion other wonders. Not to mention the packets of Fruit Pastilles, Smarties, M and M’s
[I think they're spelt "M&M's"] , Minstrels, liquorish sticks, sherbet lollies and bagged candyfloss called ‘Kotton Kandy’. Kieran absorbed each sight while his mouth provided the tastes to match. In his head, sweet tangy sherbet itched
[again, not sure if "itched" is appropriate. Others may disagree, of course] at his lips, rubbery jellied worms slithered across his tongue, and the gooeyness of creamy milk chocolate filled his mouth.
“A small box of honey popcorn please, and a bag of Minstrels,
[full stop] oh…
[perhaps a comma here, if he doesn't pause] and some sugared worms
[exclamation point if he's kind of excited and demanding, else use a comma]” Kieran said to the woman behind the counter. “What you
[I assume he doesn't say "What're" or "what are". If the speech is deliberate, leave as is] gonna have, Splotch?”
“Same as you
[comma] I guess,” Mark answered, “Can we get some tropical slush juice too?”
Kieran handed over his money, and
[you don't need the "and"] then pocketed the change: just a few small coins
[you could arrange sentence to "pocketed the minimal change he received"]. Heading to the queue for
[the] Pit of Doom, the slush juice leaked down his hand; but he noticed that,
[remove comma] somehow,
[ditto] Splotch had already managed to get a gloop of it on his hooded top.
[is this sentence really necessary? Does it convey anything important? Does it add to your character somehow? If not, try to leave the unnecessary bits out]
“You’re going to be scared out of your pants.
[coma]” Kieran said, licking juice off his hand and turning to Splotch behind him. The movie was rated for 12’s and over,
[remove comma] because of it’s mild peril
[comma] but Splotch was allowed in because
[to avoid using "because" twice, use "since"] he was with Kieran
[comma] who had just had his thirteenth birthday.
“The movie’s about kids your age being kidnapped by madmen
[comma] probably with one-arm and killer dogs who make you work forever down in a mine to dig up diamonds so the rich mine owner can get enough money to bribe the cops and do street racing in his Ferrari
[comma] and the boys that get caught
[comma] never escape
[comma] and have to live in the mine forever.” Catching his breath, a grin spread across Kieran
['s] face when Splotch stared at him with large teacup eyes: wide and scared, just as he’d hoped.
“Yeah, well, they won’t catch me if they only got one arm!” was all Mark said, and stood ready to fight off an impending attack.
The doors for cinema screen number ten opened and they rushed in, picking seats right at the front. Before him, the swimming-pool sized
[swimming pool-sized] screen filled Kieran’s entire view as the lights went out and the movie started.
[Inside his ears
= remove] he could feel his eardrums vibrating with the thundering sound,
[you don't need the next bit; it's clear the sound is loud and strong] boom…thad-da…boom…thad-da…boom hitting him from all sides as the opening title, The Pit of Doom, rippled across his vision, wavering in from the left and zooming off smaller at the top right. For one hour and fourteen minutes, giants walked
[there are much stronger verbs you could use instead of "walk"] in front of their eyes with booming voices
[eyes that have booming voices? Wow, I want to see this film! ... So the sentence doesn't mean this, maybe use "For just over an hour, giants with booming voices marched in front of their eyes]. Without knowing it, both of them had been captured, almost as badly as the children in the mines were, by the magic of the big screen.
“Hey!
[comma instead? If you do change it, put the exclamation point after "sweets"] Let’s get more sweets,” Kieran said on their way out after the movie finished, and ran to the counter watching the woman behind it pick up the popcorn scoop.
“And what can I get for you two young men?” she asked.
“Ummm, …,”
[No! No! No! You don't need this many punctuation marks! If the sentence is trailing off, just use the ellipsis (the three dots). No more.] Kieran said, dredging three one-pence coins up
[remove "up" as it's an unneeded word] from his pocket. Glaring at the coins, then up into the ladies’
[are there multiple ladies? If there aren't, use "lady's"] eyes, he said, “Uh! Nu…nothing
[If he's stuttering or correcting himself, it's a hyphen needed (the two dashes), not an ellipsis],
[remove comma] thanks.” Turning away, Kieran stomped out of the cinema with Mark closely in tow.
“Wow! That was awesome, wasn’t it,
[question mark] did you see that Farrary
[deliberate misspelling?] do that flip in the air and smash to smithereens? And that pit was creeeeeeeepeeeeeee
[hmmm... again with the elongated words...],
[full stop] I was so scared when that boy got grabbed by that big bloke… and he had two arms
[comma] he did
[comma] not one… and they were massive
[comma] weren’t they….”
Kieran was half listening to Mark’s ravings about the film, but his thoughts boiled with more-
[remove hyphen] important stuff. “Where am I gonna get more sweets from? … I could kill for some sherbet toffees, all pink and powdered in icing…
[capital letter] where did all my money go…
[comma. not ellipsis] must have been those tropical slush drinks that ate it all… No Way, this sucks!”
Caught up in movie rantings and sugary sweet cravings
[comma] they didn’t notice the difference tonight as they headed down the alley behind Vampire Steak’s Grill & Restaurant – their agreed upon route to walk home
["their agreed route home"]. Normally there were loads of people heading this way,
[remove comma] to get chips at Mario’s chip van down the other end, but tonight it was quiet,
[remove comma] and dark. The alley came out at the corner of Sweetmans
[Sweetman's?] Drive, about half a mile from Mark’s house, where Kieran could get a ride home.
“Hey, Splodge, is that a Ferrari?” Kieran asked, staring through the gloom at a sleek sports car parked on the other side of the road where,
[remove comma] Mario’s chip van normally parked.
“I dunno, it’s too dark to see properly,” Mark said
[comma] looking up at smashed remains above him,
[full stop] “looks like someone’s been shooting pellets at the streetlight again. It makes it creepy, dusnit?” Looking away from the lamp, he asked, “You think that car might belong to that evil guy from Africa in the movie, come to get us?” He edged across the road towards it.
Reaching the car together, they raised their hands against the side window,
[remove comma] and peered inside.
“Nah, it’s just one of them look-a-like
[look-alike] Mazda things,” Kieran said, spotting the logo on the steering wheel. “Still cool though.”
[I have a thing for cars, and I must say, a Mazda, even an MX5, does not look like a Ferrari. Then again, maybe the boys are not as likely to know this 
]
“OY!
[personally I'd not use all capitals here. Also, did you mean" Oi!", which is, according to answers.com "a British and Australian working class slang interjection used to get someone's attention, or to express surprise or disapproval.] You kids …
[to keep the flow of text immediate, use a dash or a comma here, not the ellipsis] you’d better not scratch my new car.
[If someone is shouting or exclaiming, use an exclamation point at the end]”
Mark thought he’d lost his shoes
[what? Oh, I think you mean that he almost physically jumped out of his shoes... I'm not sure of this line fully, though] as he jumped at the unexpected voice behind them. He saw Kieran turn around at the same time he did to see where it had come from, as he wiggled his big toe against the top of his shoe to make sure it was still on his foot.
[sounds as if you've added the foot-wiggling in as an afterthought. Perhaps make into two separate sentences?]
In the darkness below the broken streetlamp, Mark saw a dark shape moving towards him. We weren’t doing anything to damage it, he heard Kieran say beside him, but Mark could only stare. Where he’d first looked, he could now see a vague shape moving towards him. He couldn’t speak, but his thoughts raced.
“Where’d he come from,
[question mark]” he heard himself think.
[Also, since it's not direct speech, I'd leave off the quotation marks and instead italicise the sentence] “And what’s wrong with him,
[quotation mark] he looks a bit wonky. Kind of off balance, leaning to one side. As if –“
As the man reached where they stood
[kind of clunky -- and also can be cut down a few words. Perhaps "As the man reached them"], Mark gasped. He only had one arm.
“RUN!” Kieran yelled, making a dash to his left. Mark was not so lucky. The man lunged at Mark with his one remaining limb – he wasn’t a large man, but he was very fast – and his bony fingers caught Mark
['s] arm in a vice-grip
[either vice-like grip, or vice grip]. Mark’s head shook without him realising it, and the dark world wiggled around him as he thrashed in an attempt to get away - without any success.
“Now look, what’s with all this running away,
[question mark] I didn’t mean to frighten you
[comma] lads. Look
[repeat of the word "look"], I’m sorry, I’ve got some sweets here if you want some?” the man said, not really asking. His deep voice was kind of friendly
[comma] though, and Mark stopped struggling against the strong grip.
Kieran had already stopped running,
[remove comma] and
[now] stood a few feet away
[comma] looking back at them.
“What sweets you got?” he asked, stepping closer.
-o-
Two weeks later, the headline in The Powys Herald read, “TWO BOYS STILL MISSING AFTER WATCHING KIDNAPPING MOVIE!”
There you go!
Remember not to overuse your commas, and dashes are represented by two hyphens placed together like this:
--
I think one of the difficulties in writing a piece from a child's point of view is that you have to struggle between using good, imaginative description, and simple words which they would understand. I think from a reader's view I found the descriptions too weak and bland. But I assume that the work is aimed at young people anyway, not adults, so that's maybe okay.
Perhaps you could also lessen the loooonnngggg words you use -- that way it's easier to read, and the shorter words don't look so obtrusive on the page.
Also, a good tip for knowing when to use dashes: In an example like "My brother is hard-working, left-handed, and is also prone to eating honey popcorn", take out the first word in the pair. If the remaining word still fits in the sentence without losing its meaning, e.g. "is also prone to eating popcarn", then don't use the hyphen between. Conversly, if the sentence does lose its meaning when you take out the preceding word, e.g. My brother is handed", you'll know to add in the dash (My brother is left-handed).
I hope these suggestions have been helpful!
