Options:
iPhone or other android phone with a tracker APP - all that’s needed is a phone on both ends.
Airtag - requires you to have an iPhone.
Other GPS tracker - will require the tracker and an App on your phone to be able to track.
smart watch with a built in tracker - again will require a phone on your side with an App to actually track it.
all of these options rely on some type of app and wifi connection / phone signal.
Personally I would get DS a phone which is the same operating system as your yours (Apple if you have Apple / android if you have android etc), this is going to be the ideal to avoid any faff with incompatible tech / apps. It doesn’t have to be the same model.
I would then use a tracking app.
if you don’t want him to have a phone, next best is a tracker on a watch. I don’t know of any but they must exist - a Google will show the best ones.
At 11 a phone is probably a good idea but it doesn’t have to be a top of the range one. Depending on money I would combine a phone with a smart watch, sync it all up.
or do what I’m planning on doing and microchipping my kids.
joking - but I actually 100% would if it was a thing.