To do family sharing to Apple Watch or not

I feel like I may know the answer but here it goes. My son who is 9 has an iPhone SE gen 2 (parental controls enforecd) which he uses regularly to be in touch etc and takes good care of it otherwise this wouldn't be a topic lol. I was wondering if I were go get him an apple watch se cellular version if it would it be more beneficial on my end to just set it up with family sharing anyway instead of directly on his iphone Any thoughts/ advice is appreciated.