Miss Potter (2007) with Renee Zellweger and Ewan McGregor is not children's lit, but it's worthy of mention here. It's a delightful family movie based on the life of celebrated children's author, Beatrix Potter. The movie is rated PG for "brief mild language," but I think it is a wonderful family movie and can't even recall what language might have been offensive. If you're not a fan of The Tale of Peter Rabbit, you will be after watching this enchanting movie.
As I watched it, I kept thinking how wonderful it is that the Disney Company has not acquired the rights to these charming and artistically perfect characters and changed them in the way that A.A. Milne's, Winnie the Pooh characters have been irrevocably changed.