My DD will be 4 in a couple weeks. I have several apps on mr itouch for her for times we find ourselves waiting (doctors, etc). She also occasionally plays at home for small bits of time. Some of the apps I've found that hold her attention are: spinart, puzzle palace, my reef 3d, glow doodle, acrobots, volt, pollock, mini piano, bubble wrap, blowfish, dotopop, dr seuss books ( currently on sale), super why, make me a princess, match magic, save the picnic, penguin flip, hershey's chocolate milk
I grabbed most of these during times they've gone on sale or have been free. I think Super why is the only one listed that I paid full price for. Not certain of the everyday price of the others.