I think in children's books people are more inclined to stick to local books, what with them having recognizable settings, a familiar mindset, and all. At least that seems to be the case if I look at the Dutch language area - in terms of adult literature, a huge percentage of what we read is translated (or we read it in a foreign language), most of it from English, but for children's books that percentage is a good bit lower. Though if you look at picture books with little or no text, those are more international again, I guess because they're so easy to translate and publish in other languages. In the US I suppose both adults and children mostly read American books, or at least originally English-language ones (if the Newbery included British books, I'm sure I'd have recognized more).