Parents are concerned with their kids being exposed to:

Inappropriate content like pornography, gambling, violence, hate-speech and self-harm.

Inappropriate conduct like being victims of social engineering, excessive use to the point of addiction, participating in dangerous challenges, and cyber bullying.

inappropriate contact like engaging with strangers, and falling victim to sextortion.

Most online threats utilize human behavior, thus the solution has to incorporate both technological means as well as physical ones.