As a child I missed out on many classic children's books and didn't read them until I was much older. While there are many movies I have loved that were originally a children's book, since I didn't read the original they won't be included in my list.
Polyanna 1960
The Black Stallion 1979
Old Yeller 1957
Charlott's Web 1973
Harry Potter films
Ann of Green Gables
Willy Wonka and the Chocolate Factory 1971
The Little Princess with Shirley Temple