WinTalkWriter is the very best program I've ever seen for people with such concerns, easily distracted kids to learn to type and read and write words.  There's a simple screen for word processing so they don't get distracted, and the program says the letter as you type it, so they use it to learn letters and the keyboard as well.  The menu bar says the options aloud when you click or roll over them.  There are no wrong choices (so less frustration), the program says just what you type.  When you hit the space bar or return, it says the whole word or phrase.  We use it to type words from what we did that day, and she can type "play on the computer" all by herself.  Sometimes it takes a lot of repetition for low functioning kids to "get it", and this is a fun and painless way to do that.

The program includes a slide show called ABC Discovery which goes through the alphabet with engaging photos for each letter.  That one's fun all by itself.