"Slavery was illegal in England, but parents were still understood to be responsible for their children to an extent, moreso the younger the kid is. However, it was also generally understood that the younger a child is the less anyone was responsible for their actions. If a pre-teen broke somebody's window, the parents would be expected to pay to replace it and perhaps scolded for not raising the child better. If a teenager like these children did that, the teen themselves would be punished, more likely, the fine would be harder, perhaps either the child or a parent would be jailed or punished with lashes, and also made to pay to replace the window. As an aside, it's considered cruel to punish women with pain, but not for men. But that's irrelevant."
"In this particular case - teens over fifteen, assault and removing people from public places? - The parents would possibly expect their children to be jailed, and for them to be alerted by the police that their children are in trouble, but not arrested themselves - and eventually the child goes before a judge and the judge decides whether to sentence the child to jailing or labor in a work camp or, if they were not particularly poor, a fine which the parents would pay. And in any case, the parents are likely to punish the children themselves when they're eventually returned."