Use the e-mail that identifies you as a human being — your personal one. Avoid shared, work or role-based addresses (like info@ or team@). You will use this e-mail every time you sign in.

If your child doesn't have their own e-mail, you can use the yourname+childsname@gmail.com trick. Most providers (Gmail, Outlook, iCloud, Fastmail and more) ignore everything between the + and the @, so the e-mail still lands in your own inbox — but it counts as a unique e-mail here. That way you can manage your child's account without creating a separate mailbox.