Would you have told these children off or not?

No. Children should be taught right from wrong. Throwing things at people is wrong and that type of behavior shouldn't be excused. I definitely believe in strong discipline. I would not only have scolded them for doing that but I would have also made them apologize. I guarantee they wouldn't have done it again. If they cried, it's ok that means they get it, they understand they were wrong. After teaching them that lesson they would be free to return to play as normal.