How to implement parental oversight for web user accounts?

Say, a mother has an account on an educational web platform. She now wants her 12 year old daughter to also use the platform. But as the daughter is a minor, her mother wants an oversight into the daughter's account to identify bullying, threats and abuse.

How would a web authentication and account management system be built for this requirement? What should be taken into consideration when building such a system?

One way to achieve this is to let more than one person access the account(in the above example both mother and daughter can access the daughter's account, even simultaneously). But this could give rise to lot of security issues. How does one mitigate that? Or are there better ways to implement parental oversight into web accounts?