I don't know how long you have been using computers with your PreK students, but have you talked to Neil at Sunday Software for software ideas and best practices for working with PreK?

I'm also thinking for the money it would cost you to buy touch pads you could make an amazing room specific to PreKs, like an amazing storytelling table with lots of cool story props, so they could re-inact the bible story.

I came across an apps program on the Christmas Story.  Out of curiosity, I had a friend, who's also does Rotation check it out for me, as I could not - she gave it a definite two thumbs down.  She has regular games she's downloaded on her Touchpad for her little grandson which all had way more features and games for a quarter of the cost, said it wasn't worth the money they were asking for.  The site was 3D Digital Bible Books (since this was posted this site is no longer active).

The problem is that for someone to market it, there has to be a buying market, and the Christian Market is not very big!  So you have to look at the cost to create something and what your returns will be.  You are also looking for material specific to PreK so again you've really narrowed the market.  I know, I work in a Christian Bookstore.  And computers labs in churches is again a small market.   And generally Christian publishers prices seem higher, but it's due to the smaller market and they like everyone else have to make a living.

Sorry, I'm not much help as I can see you want to involve the kids in the computer lab and wish you the best of luck in finding a solution that works for your church.