Well, I'm 6ft even (if I stand up straight) and he only comes up to my mid torso. We've tried adult sized glasses... and they're waaay too big. (But they do make him look kinda silly
). Looking like he'll be okay with regular sized muffs. So his mom can buy him whichever she can find.
The biggest issue, now... is finding an appropriate rifle to borrow. Even our 10/22 is too long in LOP for him.