We still wear ours in situations where our youngest needs to wear one. He is partially vaccinated though so we have an end in sight. I don't think he really cares though and would understand if we were mask-free and he wasn't. Most kids are pretty flexible and not nearly as bothered by mask rules as some adults are. I know it varies by state but our kids have been wearing them all year at school, clubs and sports.
My youngest is 8, and with two older siblings, he's well aware of where everyone in the family is with regard to vaccination - I don't think he'll have a problem wearing one indoors even if the rest of us aren't. Like yours, he hasn't had a problem with it all year - he's the most likely of all of ours to leave it on even when he doesn't have to.