How big do you like your tablet? If you're designing a kid-friendly device that can be used as an easel, learning resource and game platform, the answer is probably: roughly Monopoly-board big.
No, 10 or even 12 inches isn't going to do it for you. You're going to want a device with a 20- or 24-inch display, like nabi's new Big Tab tablets, made by Fuhu. The Big Tabs are the biggest Android slates we've ever seen for sale (although there have been demos of significantly bigger models).