hm..... I bought one for my kids (4 years old, 2 years old and 1 year old), everyone says I am crazy and would ruin my girl. However, I use it to be an electric book/flash card for them, they like the function of "read to me" and after that, they will pretend a teacher to "I read"...... and my girls learn a lot of new terms in PTH and English, which are good for them.
But I agree that they will easy addict to the iPAD, so control it.
In addition, don't download to much games for them, I hate people keep playing game.....luckily, they don't like as well. They like reading books/ stories much.