Our oldest child's kindergarten class (at a very rural, poor school) was doing multiplication and division within the first month, because they all attended a pre-k that encouraged the use of educational games, like Prodigy for math.

Like everything, It's what is on the screen and how the child is using it and how involved the parents can be. Number blocks are the same way. They're a great way to learn basic reading and writing, if that's how the parents use it; they are also a great chew toy without some input from the parents.