One possibility: hold executives, product managers, and engineers personally criminally liable for building a system that puts inappropriate material in front of children or connects them with predators, and let them figure out how they'd like to avoid that liability. Could be through building something more robust (e.g. only allowing kids to play with pre-whitelisted friends, not any anonymous user), or hiring a legion of moderators, or through not building such a platform at all. That's up to them.

We don't need to prescribe what they ought to do. It's sufficient to say what we have here is unacceptable and make fixing it be a them problem.