A:Answer Good questions!
I guess my first question to you is how old are the children? Are they going to be gaming, or are they just going to be looking around, viewing movies, pictures, etc. Light gaming would be fine with this, but if your children are into gaming specifically, then I would not recommend this unit (you may want to look at the Quest for that).
As far as how many, I bought 2 thinking that there would be 2 of them using it constantly. Turns out only 1 really likes it, and the other is not as interested. So, 1 unit is fine for my situation. It was easy to return since it wasn't even opened.