Participating in online communities is a fun, fulfilling and mostly harmless activity that improves many young people’s mental health, creativity, communication skills, and probably has other benefits too.
It should be, it was, but thanks to a bunch of billionaire technofeudalists it's now infested with dark patterns, engagement algorithms running on fear and anger to drive addiction, propaganda, segmentation into unhealthy 'echo chambers' and whatever else they've cribbed from tobacco marketers and evil psychologists. There is significant scientific evidence that it is indeed harmful to children especially, but also adults.
The needful target is not keeping it away from children. It is fighting to bring down the Metas, the Xitters, the TikToks and YouTubes, ban the algorithms that they know full well are harmful to all. We need hold the companies responsible for those harms and fine them until there eyes bleed, but most importantly we need to hold the individuals in charge personally responsible, take away that 'the company did it' excuse. Have them rot in jail for the term of their natural lives as an example to all who would follow.