Why stopping children from using techs? Show them the most valuable and interesting ways to use them. Buy them devices, which are less hurtful for health and eyes.
Also, teach them how their emotional system works, and what makes people more or less successful in life and in games. Teach and train them to manage their desires and emotions so that to be happy in life, "here and now" and in the future, and successful in their goals and wishes by using techs and without them. If you don't know that yourself, use compenent psychologists for that.
Apply techniques of cognitive and behavioral therapy and methods of direct influence on emotions, and dopamine trainings to prevent neurotic behaviors and over-dependency from opinions of peers and techs.
Offer games that allow children to become self-determined, and happy as they are, not dependent of opinions or anything.
Make sure children get enough of love, respect and moral support in families. This prevents most of problems, whatever.
Teach parents about the most essential psychological needs of children to make sure the children are satisfied as for these needs. When children are satisfied in love, hugs, respect, freedom, diversity, a feeling of the better future, support from the relatives, all kinds of ill dependancies from substances, games, TV, people, food, etc, are much less probable to develop!
Starting from 10-13, help the child to build his/her life strategy, to dream about the better future, and build a plan how to achieve it. The plan should include items which are pleasant or at least not disgusting and annoying to accomplish for the specific child.
Make sure the child has enough of offline interesting games and other opportunities to spend time with his peers. This will compete with Minecraft and Roblox.
Make sure your children most of time in the day have an adult person around, very interesting for them. It may be a teacher, tutor, adult friend, or a neighbor.
Now I can say a very strange thing: the pedophiles are often the people who can make children interested in communication besides minecraft. I do not mean sexual interaction, but sublimating the sexual attraction to children may lead to being a loving and motivated person who is really interesting for children. This is not my idea, it's from history. Many of the most outstanding pedagogues were either pedophiles or latent ones. This is the same in all countries.
This is quite a surprising but true thought: punishing, condemnation and fear of pedophiles leads to overdependancy from minecraft and social networks in children. Use technologies to control that pedophiles do not do anything hurting the children, and then bring them into contact with children as much as children want. This will distract children from gadgets and give an urge to their personal development.