I read somewhere, george acknowledged how JK Rowling 'aged' her franchise along with the audience -- the first book/movie was aimed at a fairly young audience.. but as the years went by, and she released more books, the story grew more mature as it went along. to the point where, the latter harry potter movies are too scary for little kids. but the first ones are just fine.
George always intended for ROTS to be PG-13. counting backwards, at a rate of 3 years between movies, he intentionally aimed TPM at an audience of six year olds.
they say, this was his intention for the OT as well, but the "suits" at Fox steered it more towards the 12-year-old male demographic instead. thankfully, it caught on with younger kids too. (I was 7 and it suited me just fine). ;) later when he took control for ROTJ, he went back and tried to cater to that 'teddy bear' audience all over again, but, by then it was too late. his '12-year-old-male' was now 18 -- the core audience had little patience for teddy bears. aiming 'old' to start and 'young' to finish, didn't work as well as what rowling did.
--> for the PT he took a page from Rowling's book and aimed young to start, old to finish. so to speak. (he aged the franchise along with his audience).
-=-
in the end, history reveals that the OT caught on just fine with the 5-7 crowd ;) and TPM is aimed at the 5-7 crowd. 8)
the only one you really need to be careful of is ROTS. :-\ (and only because, he did that on purpose, with ham-fisted subtlety) :-\