I actually don't think this looks that bad. I think it might even be good for them. If young people are eschewing helmets, I can see making a helmet law, but even if they take over a lane of traffic, they seem to be going in such large groups, that if they'd been in cars or other vehicles, moving in the most orderly manner imaginable, they'd be blocking the intersection just as effectively.

Consequently I think this is mostly fine. The big problems are the helmet issue and I also think they might need knee protection. 60 km/h is a bit high if they're made for 25 km/h, but most of this stuff is achievable with ordinary bicycles.