Starfall ABCs is a great free app for students to learn and interact with letters and sounds in words, sentences, and games. The app can be used anywhere your children are learning and playing; no Starfall membership or internet connection required!
Check out more info here: http://more.starfall.com/info/apps/abc.php
Download from the app store here: https://itunes.apple.com/us/app/starfall-abcs/id395623983?mt=8