Many children I know from the age of 1 up love Elmo. This app by Sesame Street uses Elmo and other characters from Sesame Street to help children learn the ABCs.
The app is packed with activities and games including tracing the letters (both lower and upper case), videos where other Sesame Street characters or Elmo show objects that start with that letter, and coloring books where you drag your finger to color the objects (again that start with the letter).
It also has an activity where the objects are hidden behind either bubbles, leaves, or balloons. And you use your finger either to pop or rake them to find the hidden objects. Smaller children lose hours doing this.
My complaints are minor, but enough not to give it 5 stars. No android version exists. The application is very large and not only does it take a long time to download, but also takes up a lot of space on your iPad. Although kids love Elmo’s voice, it will get irritating to the parents quickly (especially since on some activities Elmo repeats the same phrases over and over). Some of the buttons are not clear and might confuse the younger children (the slider is hard to master, and the function of the star on the left bottom is not clear).
Overall a great app. I would highly recommend getting the free version (limited to the first three letters).