Beswitched, the staff simply aren't paid enough to police their workplace. They will be following the rules management have dictated anyway - usually no response unless there's a real hazard.
Why should they intervene on your behalf? Be strong and confront the parents (I often have) or just put up with the disruption. that's your choice.
A friend went to a carvery for lunch - then complained to staff about unruly children! Staff response was that it's a family restaurant and they were entitled to enjoy themselves too. My input - 'What did you expect? Choose somewhere else if you value peace and quiet'.
Fashion for short, overweight woman
Being quizzed by chemist's assistant in Boots.
To think that London, or anywhere else for that matter, does not belong to any one demographic