I think this is less "how can we rip kids off as much as possible" (see: Beanie Babies, pogs) and more "how can I make something that would have blown my 8-10 year old mind?" (see: Pokemon.)
That doesn't mean clever marketing isn't part of it, but if the people are making something to sell a lot it will fail. Kids can sense that. It has to legitimately be fun and something of a labor of love.