I agree that the Film is aimed at kids, but the books are read by all age groups (even I have read them). Therefore, the film should perhaps have been a little better thought out.
Hermione is meant to annoy - that's the whole point of her character, and to be a smart-arse. Harry himself is a crap actor - and he is meant to have messy hair. Ron, well, apart from the Steve comparisons, is annoying as hell.
But the film switches between scenes at a stupid speed, over extends things that don't need it, and cuts out some really important bits. The mess of actors completely fail to work together. I can only assume that (like Gormengast) these actors were in it for the entry on their CV.
LotR is actually a kids story too. Remeber also, that Jurassic Park was a PG. The rating is simply the minimum the film will get away with - the Producers don't want to limit their audience, and being as the books featured very little gore (violence, sure, but no gore), no sex, and no bad language, why not make it a PG?
I wish it was a 12, or 15, though. They could have done sooo much more with Liv Tyler.... mmmmmrrrggghhhhhh Liv... drool.