It'd be fine if they were just using chat apps. It's not the communication that's the problem, or the bullying. That's going to happen regardless, and it's nothing new to online spaces. If anything, having online spaces available is helpful, because kids who are excluded at school are able to find places they fit in online. It's the algorithmic feeds and short-form video content. It's flooding their brains in their most formative time.
I think being contacted by or contacting strangers is also a separate concern. Bullying is also a problem.