From the apple store the endless alphabet app is free for now (idk for how long) I just bought this a few days ago I really love it. It has cute monsters and and huge range of vocabulary and the letters make their sounds when you drag them to the word. After you finish the word it then gives a short description of the word like hilarious is a word my 2 year old was just piecing together. I really really like this app so far. Idk if they have it for kindle or android but it doesn't hurt to look.