If your first reaction to this app is "Why would you let your toddler play with your $300 iPhone?", well, it's pretty clear you don't have kids, so you can skip this story.
For those who do have children in the 2-5 year old range, Whizzit 123 seems to be the functional equivalent of Doodle Jump that has them coming back again and again. The game simply consists of different objects that are presented in quantities of up to 10 or 20 based on a user selectable option, and the child simply taps on each one as they are counted out loud. Each item displays a brief animated flourish as they are counted. Each tap offers a small animation and the final tally is repeated out loud at the end. That's pretty much it.
It's fun, educational, and strangely rewarding. My daughter rates it as "Yay!"
App Store Link: Whizzit 123, $0.99