I don't know if anyone her posted about this already, as a search for "epic" even when paired with app or itunes brought up tons and tons of posts, but none that seemed relevant.
There is a new-ish app on iTunes called Epic! which is a reading app for kids. It has a ton of books and they add new ones every few days. My 5yo reader loves it. He's been reading a lot of books about science -- astronomy, levers, lightning, animals, etc and has new facts for me every day. There is also a lot of picture books and fiction chapter books.
It costs $5/month and is worth every cent. I figure that's the cost of one book and he has a library at his fingertips. We just went on a short vacation and instead of packing a bunch of books for him all I had to do was bring the iPad.
This is the app if anyone is interested:
https://itunes.apple.com/us/app/epic...ds/id719219382
I have nothing to do with the app or the company who makes it. I'm just a really happy customer.