In some cases, you won't be asked to enter a PIN even when a profile is locked because:
Some devices can't be updated to require a PIN to enter locked profiles. On these devices:
The Profile Lock PIN isn't required to access a locked profile, but is required to watch TV shows or movies in that profile.
You can’t add new profiles if a PIN is required to add profiles to the account.
Some web browsers automatically open a locked profile when you sign in.
The web browser automatically opens the last profile used. If you don't want to be automatically signed in to the last used profile, clear your browser cookies.
Your account password is still required to sign in and access the locked profile.
Anyone with your password can change parental controls.