Home school the children!

Take control of the Internet (firewall and DNS) and don't allow access to social media or a smart phone until appropriate age.

Teach the children about these problematic issues so they actually understands why they can't have free access to a smart phone, and what's really bad about the Internet. Make them understand these issues!

Make contact to other people who do the same and let the children's social contacts be with like minded people in real life.

We, and several other families, have done that, and are still doing it, with great success.