Google family account takes over browser - stop automatic login

I log in with several Google accounts, one of them being my sons school account. Then when I do a search, I get a message saying that I can’t go to that page. In the url it says https://families.google/ … I then go back to log out from his school account (which uses families), but nobody is signed in. I then click sign in because I figure that will get rid of the problem. That, I cannot, and I end up on the login page to his school account. I stopped using safari and went to Firefox to avoid this exact problem and now it is happening again. It is seemingly autologging in to the school account, and they have restrictions on that account that won’t let them surf ads. How do I stop the automatic login?