Here are some fun (and some educational) ones....
*Bubblesnap (free) is one of many shrink-wrap popping apps that, for some reason, are equally as addicting as the real thing.
*Balloonimals ($1.99) even better - make balloon animals!
*Wheels on the Bus ($.99) is an electronic pop-up book, where users drive the action by touching, swiping and tapping their way through the familiar preschool song. Ages 2-5.
*iWriteWords ($.99) turns the letters of the alphabet into dot-to-dot puzzles. Ages 4-5. A more limited lite version is free.
*MiniPiano (free) is a 14-key keyboard
*Scoops ($.99) lets you tilt your screen left or right to sort falling scoops of ice cream. You can make patterns with same-colored scoops, while dodging the veggies. Ages 3-up.
*iPrompts ($49.99) "Thousands of caregivers use iPrompts® to provide visual support for those with language and behavioral challenges, including autism and ADD/ADHD. Acclaimed in news stories around the world, iPrompts® also works great with typical kids!"
See also THESE iphone apps recommended by RedTricycle!