How do I switch the iCloud user from child to parent on iPad?

I have an iPad that was formatted. I created an iCloud account (under family sharing) for my son who is under the age of 13, and logged him in this iPad.

I want to log him out and log into the iPad using my iCloud account.

Problem is, when I go to Settings/iCloud and then sign out in order to sign him out, the "Sign Out" button is grayed out. Says "Sign out isn to available due to restrictions".

How do I sign him out, short of formatting the iPad over again.