This is a great idea, because I'll be able to snag a free Apple watch ;)
I regularly have phone watches left at our house by my children's friends and if you walk through the school after hours you'll occasionally find one lying on the floor (in amongst all the discarded clothes). They're too big for active children to want to keep on all day.
I can see why this would benefit some people, if their children have long solo commutes, and I'd trust Apple's privacy features more than most other phone watch manufacturers. But in general I'm more in favour of free-range children and not being able to track where my 9 year old is or have them message me every 10 minutes.