I have this app installed on my phone. When you sign up you purposefully have to get consent from an adult to sign up as a minor.
In that sense, it shall be treated as if there hasn't been a contract at all. The process is purposefully designed to get a signed contract as fast as possible. The technology to make proper ID (Age) verification is available, but my understanding is, that it is not used by facebook and its partners.
I mixed two points here. Contracts that contradict the law and my wish for better regulations.