Hello, thank you for your help!
Is your son's account a child account associated with your parent account?
Yes, and parental consent settings have been configured following the URL below, and we're all friends.
If your wife hosts a world can your son join that, either before or after you do?
Yes
If your son joins before your wife does it work?
Son is unable to join at all presently. However, he would normally join after I start the world and my wife would join a bit later. It's rare that she joined before him, until after he was no longer able to join. One of the times I was able to somehow fix it for a session and she was already in the game.
Also, if I list all players, he is not listed.
If you create and host a brand-new world, is your son able to join that?
Yes, and he can access pre-existing games.
If so, does that work just once, or every time?
Every time. We have not had an issue with joining other worlds; only our fun Family Survival world.
Thanks, Ooofboiz, that seems to be exactly the bug. I changed from the Alex skin to Steve and he could join the game again.
Before your response, I decided to try the world in Minecraft Realms. He was able to join the Realm with the Alex skin without incident.
I appreciate everyone's help here!