What protects children is communication with their parents, not that third parties can read their messages
I don’t support weakened encryption, but parents are very much part of the problem.
In the set of parents, we find problems and solutions.
Because of this reality, we can know that simply "having parents to talk to" cannot guarantee a solution.
The same pattern is present with breaking encryption: it gets us to a solution: allowing law enforcement to invade the communications of perpetrators. It also gets us to a problem: allowing perpetrators to invade the communications of children.
We can't simply choose the outcome we want and ignore the other. Both are strongly predictable. That means this strategy is not worthwhile.