I haven't read any of the books, but i've seen all the films so far. Three is the best, so if you only watched up to 2 and gave up on the films, you are missing the best film of the series so far imo.
Love the books to death, the films are ok - as others have said they don't do the books justice at all.
They do start out a bit children's books-ish but do get darker and a lot more involved as they go on. From GOF onwarRAB I would not say they are necessarily children's books.
I do object to being called 'strange' by people that have never read the books or have only seen the films. A lot of immensely popular (with kiRAB and adults) books are children's books - or have at least started out that way and I think its really judgemental and intolerant to be labelled because I am and an adult and I happen to enjoy the books. Just as I think its judgemental and intolerant to judge those who don't wish to read them.
Can't wait till my daughter is old enough to enjoy them!