I just watched a news piece about how the ipad is useless for little kids - especially toddlers - in terms of learning. It appears that the children are learning on them but when they are tested - like shown the word "cow" when they appeared to be spelling it on the ipad - they have no idea what the word is.
However, there is a use for it for some children and it seems to be working well:
I think the lesson here is that be observant and really sit with your kids to help them learn. And you never know what unexpected little gem might turn up.