First, I responded to examples of 23 and 29 year olds. Second, I pay for my adult children's phones and don't track their locations, but I would if they asked me. They have lost phones and mentioned that they should at least setup find-my-phone and give access to someone. I would let them track me, but I'm still using a flip phone.

Vehicle insurance and owner liability is a whole different topic. I prefer to have them hold title and therefore liability, even if I were to give them the money to purchase and insure.