I want a dedicated hand-held that does video, and can lock the screen while maintaining video input and output.

I have a 16 month old kid; she has grandparents who are in various stages of decline, from "knees and back hurt a little" to "fairly advanced Alzheimers", and with various levels of computer expertise at the best of times.

I want to send each of them a tablet that someone configures once to be on wifi, and then just lets them receive calls from me, or the kid. I would also like this thing to be something sturdy enough I could just give to the kid so she can run around with it, and drool on it, without disconnecting the call until I unlock the device. (Grandparents aren't at the drooling stage yet, but at least one is likely to leave it outside in the rain.)

Does such a critter exist?