This is a carrier in the USA (T-Mobile).

I did a quick search for the other 2 carriers using the term “[Carrier Name] Family Tracking” and Verizon and AT&T also seems to have it.

And according to https://www.t-mobile.com/support/plans-features/t-mobile-familywhere-app, it says:

FamilyWhere uses geolocation data from the T-Mobile network and is not affected by changes to device location settings.

So it appears that its using cell tower triangulation. Turning on Airplane Mode should stop it (assuming there isn’t a separate tracking app on your phone)

Oh Wow, What a wonderful tool for abusive spouses and abusive parents. And telecom companies are making money off of it. 🙃

TLDR: Its a good idea to get your own separate cellular plan.