Why not get the young tyke a 3000 twin? He will have it all the way through college and get a quality sleep when he starts school. Never buy a used mattress. There is a reason someone is selling it and it usually has to do with "comfort". Craig's List? I'd be afraid of remnants of God knows who's DNA on that thing! I can't tell you how many parents have a 15 year old mattress, buy a new one, and claim their old one is going to their kids. That's almost criminal in my mind!