I don't know what kind of games you could fit on a watch (Tamagotchi type things?), but getting kids to actually use things requires them seeing some sort of direct reward.

We bought cheapo dumb phones for our kids and they'd never remember to take them with them, but once we were forced to get them smart phones suddenly that was never a problem.

And by forced I mean the endless wearing down of the whining and crying and petulance because all their friends had smartphones. Ugh, one of many occasions where I failed as a parent.