[kognate]

A cellular enabled Apple Watch might be a good choice if they can wear/charge a watch. It's pretty easy to navigate and doesn't require them to have their own phone. It's pretty easy to send text messages with one, too. As for the pre-paid issue, watches are often ad-ons (in the States at least) and are (usually) not expensive.

There are also a couple of companies that sell purpose-build wearables for this, but their privacy situation is sometimes murky.

It's probably worth buying the cheapest pre-paid android phone you can and doing some test runs. When my kids were that age, battery management was the biggest issue we ran into (that and trying to explain Spam calls).

[gehwartzen]

Good point on starting with the cheapest option to start just to see his needs/capabilities, thanks!