iPad games / books for kids

My nephews (4 and 6) are getting an iPad (4th generation) for Christmas and their parents want me to set it up (iTunes account, install apps, books, etc) for them when I visit for Thanksgiving.

Can anyone recommend any good educational games / children's books?

I highly recommend the Toca Boca games. Like Toca store, Toca Tailor, Toca salon, etc. Don't know if they're still on sale, but they were running for 99 cents. My 3 year old and 6 year old love them.