All the Star Wars original films were loved by children - I was five when the first came out. So unless Harry Potter would be better with Barney, your thesis doesn't work.
Actually, I'm making a distinction between a film that is widely
enjoyed by kids, and a film that is
aimed at kids. Just because kids like the first Star Wars doesn't mean the producers were actually aiming specifically to appeal to kids. If they were, that does change things for the theory. But whether kids like a film or
not, the fact is different decisions are made depending on the audience the producers are hoping to snag.
In any case, I'm not even suggesting anything along the lines of The Phantom Menace being
better with the addition of Jar Jar Binks. I'm not particularly enamored of the character myself. I'm just a little confused by the chorus of dislike for this one (as far as I'm concerned) more-or-less harmless character. Also, I agree Harry Potter would probably not benefit significantly from the addition of a magical purple dinosaur who sings songs and teaches basic schoolyard rules to children under six years old. If only because none of the characters would listen.
Come to that, I think the theory's really only strengthened by the Barney analogy. Barney himself isn't a particularly bad character--in his place. But to put him in Harry Potter and expect people to take him as seriously as everything else, that's a mistake. I agree it would be a similar mistake with Jar Jar.
I'm just not sure that he
was intended to be taken as seriously as everything else in the story.
That's just the way it came across to me when I watched it; I'm honestly not defending the character, or suggesting anyone should actually
like him. I suspect he's too far gone for that! I'm just wondering about the existence of an
additional reason for all the hatred, another ingredient in the chemical disaster known as Jar Jar Binks. Switchbacked expectations make up an equally valid reason for disliking the character. But I simply don't have a lot of context for identifying how
much they overall played into Jar Jar's epic fandom-downfall.