A child account can currently only be linked to one family account. If you are attempting to add your child’s school account to your family, but are receiving an error message noting ‘This child is in a different family. Please remove them from that family first’, this means that the account is currently linked to another family.
It may be that another member of your family has already created a family account. Check in with other family members to ensure that this hasn’t been created without your knowledge. You can remove a child from an existing family account by following the instructions here.
If you’re uncertain which account they might be linked to, you can have your child log into their account and view the listed family name. Follow these simple steps to check: