Automatically logging family member in on my device

My son and I are trying to play a friends match. I will be logged in on my iPad, and then he enters the app on his iPad and it automatically logs him in as me, and then I get kicked out of the app because it says I’m logged in on another device. He logs out (as me) and logs back in as himself. Then I go back into the app on my iPad and it will automatically log me in as him! And then he gets kicked out of the app on his iPad because it says he’s logged in on two devices. This is happening over and over again!!!! It’s very frustrating!!!! He has a child account connected to my parent account… Does that have something to do with it? I have actually never physically logged into the app on his iPad with my user name before, yet it will still somehow automatically log him in as me on that device! It is very weird, and it is making it nearly impossible for me to be able to play against my son.