Cowly Owl makes adorable iOS apps for kids. I loved their Makego app, which turned an iPhone into a little race car. Now they've got a new app called Little Digits, that teaches little kids how to count on their fingers.
Using the iPad multi-touch screen, Little Digits displays number characters by detecting how many fingers you put down. Children can learn to associate the number on the screen with the number of fingers they place down, whilst enjoying the unique characters and animations of the Little Digits world. There are also games that introduce small addition and subtraction calculations, where you can work out the answer using the same multi-touch finger detection.