I hated tuning my first violin, but got better at it. Talking cheap school violin. Then had one of my own to which I insisted on adding the fine tuners.
So you can tune a violin just on pegs, but it can be stuffing annoying. The pegs don't always turn very easily, or having turned them, they slip a fraction. If it is a violin you are going to be using for a bit (as in it will be "yours" for a while), then you can take the pegs out (one at a time, you do not want to de-string a violin in its entirety if you can avoid doing so as that can cause problems with bridge and sounding post) and if the pegs stick, you rub them with chalk, if they slip you rub them with rosin dust.
But with pegs that stick you can be trying to turn the peg ever so fractionally and when you finally get it to move, it goes too far. Very gently pulling the peg a fraction out of its hole can help, then pushing it firmly back in.
There are violins with well behaved tuning pegs.
Also note - you are talking wet drizzly day - you'd need to be out of the rain to play a violin, and certainly to look after a violin. You need to rosin the bow - block of resin that all violinists keep in their case - often a little compartment in the case for it. Can be down to sad scraps at times that you have to hold between finger and thumb and struggle not to drop - then you tend to run it up and down the bow, rather than the bow up and down it as you would do with a nice new block. If not enough rosin on the bow, it slips around. You also have to tension the bow strings by the way - turn a knob at the end to tension the horse hair. When you finish, you slack it off before putting it in the case.
Another thing - shoulder rest. If he is putting the violin on his shoulder under his chin, and not holding it lower, folk style, then you need some sort of padding between your shoulder and the instruments. The classic one for kiddies is a little square cushion with an elastic loop on it that you hook over the chin rest. But you make them to fit yourself (or your parents do), so you might need more or less padding. They also can be slippy and you don't have such a good grip on the violin. On the teacher's recommendation I had a fancy one that was an oblong metal frame with feet, with rubber strips and rubber feet that gave me a much more solid hold on the violin.
Finally - if the strings are the old "catgut" ones not modern metal ones then they will stretch in wet weather.
Also, if the instrument has been out of tune for a while, whether or not you are talking metal or catgut strings, then when you get it in tune, you will find it goes out of tune again quite fast - as in while you are playing, because the strings stretch a little under tension and if they've not been under proper tension in a while they may relax a bit on first tuning and you have to retension again.
). You pluck the string as you go to hear the change. Despite playing for years, I never got good enough to tell when it was OK by ear, so I used a tuning device that tells you when you've hit the right note. The right ones being G, D, A and E on a violin.
