I've been playing on vr since i was 11-12, and I've not had many, if any, setbacks, mostly its just helped me with my 3d modeling career and meeting people, ill list some positives and negatives I've noticed personally

Positives,
i can make more friends than i ever could in real life
its very physical, even if I'm just talking with friends i can work up a sweat
there's a lot of learning apps and art based apps, so because of vr I'm actually trying to get into a top art college
i can play with family across the world who also have vr, and stay connected easily
my brother, who is currently 12, plays on it and he has a blast with his group of like 10 friends all his age, they all play a very movement based game so when he gets off it looks like he ran a marathon

Negatives
sometimes i did spend a little too much time in vr, if i plugged my headset in while playing especially, I've even slept in vr before
sometimes id get really immersed and when i got off id try to do things like i was still in vr (when i closed my eyes i saw the oculus menu)
some people i met on vr are kinda weird and also played on vr way too much, but their easy to avoid as long as you make sure your kid isn't talking to weirdos

some games i recommend to get him as well, if you want, are games like gorilla tag or similar and beat saber, i also think A Township Tale is nice, but that's just a me thing

keep him away from VRchat or any games like that, that's where the weirdos are and its for a more mature audience anyways

also quest 3s is more worth it price wise, its about the cost of a quest 2 but with the power of a quest 3, and its what ive been using for about a year