the way i would do this is:
create a column in the users table for each class room:
in each of those columns, set the value to 0 if the user does NOT have a child in that room, or 1 if they DO.
in the Authenticate user behavior, on the third step, select each of the room columns to have them stored in session variables
create an authentication rule for each room using the session for the corresponding room and allowing if that session is equal to 1