No they didn’t have any LEGAL power to do anything. The power of violence (which is what you’re describing) is a NATURAL power, not a LEGAL one. These little shits caused as much, if not more trouble than they might have ever stopped.
We could discuss whether the police should have reacted differently to the protesters, but the reaction of police does not deputize a minor to suddenly take on police powers. Especially since I believe these folks were told by the police to go home early in the evening.