When folks ask about iPad and iPhone apps, it’s hard to pick a few to show because they do so many different things. If I show you two, the four I don’t show may be the ones that look worthwhile to you or interest your child. Nevertheless, here is one favorite,iWriteWords. There is a free version, with only 3 letters, here: iWriteWords Lite.
For those who cannot speak, check out Proloquo2go.