[morninglight]

While living in Japan, our kid used a cellphone with 3 buttons.

1. Call mom, 2. Call dad. 3. Call Auntie.

These kid's phones were very common, inexpensive and worked great.

[imp0cat]

There is an entire ecosystem of kid's watches which do exactly that. Pretty much just a miniature cellphone with restricted functions that goes on the wrist like some sort of a tracking collar.