On a LGW to MBJ, we had Y seats in front of the overwing exit (747) and by the toilets. Soon after departure, four or five small children started running up and down the aisles and in and out of the toilets. Their parents no where to be see. Then they sat down on the open space in front of us and were reasonably quiet as they played games - until the next time for running up and down.
The helpful CC aplogised and said, "I know from bitter experience that if I tell the parents to mind their children - I'll get a great mouthfull of abuse"
That was 1989 and I doubt that things have improved since then.