https://wccftech.com/facebook-instagram-booting-underage-users/

Facebook can lock you out of your account if you are below the age of 13 and using Facebook or Instagram. While everyone knows kids use these social media platforms despite their age requirements, the social networking giant is now taking a more proactive approach to enforce its age policy.

Previously, if someone reported an account for being potentially used by someone underage, Facebook had to investigate and lock the account. However, going forward the company will lock the accounts if its reviewers believe an underage user is managing it even if it hasn’t been reported for violating age policy.