Actually the ground ‘security’ was called ‘first’ who could not break up the fist-fight among the kids....THEN police were called.
From my experiences with private security, unless they are an off duty officer, most times “interaction” is shifted to the police. Observe, possibly interact, but ultimately if you get the police involved you limit the liability faced by the security firm or the property owner. It because assault on an officer the moment they throw a punch. Not so if they attack a private citizen (even working in a security role).