For me it's a slider, the older the more responsible, at 15 I would agree with you, but 10 I definitely think the parents should be the ones in court.
Would the monkey really be put down tho ? If it still holds the flamethrower of course, because it's still a threat, but after the fact I don't think so.
Of course kid can do fucked up things, but at 10 years old I disagree, she heard that somewhere for sure and isn't smart enough to be held responsible.