Wikijunior Colors is one of my favorite books at Wikibooks. It's such a simple concept, and such a fun example of how to quickly and easily create books for young children. It's also a good example for how Wikimedia projects can interoperate, with the majority of the books content being images from Commons.
Well, I saw today that there are at least three translated versions of this book: Romanian, French, and Polish. This makes good sense to me, there is very little text so very little effort is required to translate it into other languages.
If you haven't seen it yet, this is a very fun little book and almost rediculously simple in concept. A perfect way to spend a few minutes with your young children looking at colorful images.