We travel on Brittany Ferries Portsmouth > St Malo five times a year, overnight crossing.
The French kids are infinitely better behaved (yes, I generalise much), and clearly identifiable by these characteristics: they use cutlery, they don't mess around with their food & drink, they speak reasonably to their parents, siblings & anyone who speaks to them, they finish their plates then sit, relaxed, with their parents who are clearly 'in control' of them, for want of a better description.
Many (but NOT ALL) English-speaking children, in sharp contrast, end up with plenty of spare space around their families' tables due to their tendency to stand on the seat, mess around with their food including throwing it, argue loudly & pointlessly with their parents, siblings & anyone else, leave most of their food, then demand loudly to be taken to the shop / cinema / childrens' entertainment areas, heedless to whether their parents are able to enjoy their meals or not. They are frequently still running around in nappies and/or pyjamas doing the circuit at midnight, having set sail at 8pm, screaming, bodies covered in facepaint & generally wrecking anyone's chance of a relaxing evening.
The French children are usually in bed by 10. We then have a repeat performance at breakfast the next morning, to the point that we now get up early, get our breakfast & eat it outside on the deck, weather permitting.
I have brought up three children, travelled the world with them including long-haul, boats & cruises, and am a teacher in a very deprived area, so I am familiar with the challenges children present.
However, I am speaking as I find, and wish it could be different for the parents from the UK, who often seem to lack the ability or will to deal effectively with their children in public.
The French passengers and staff treat the whole pandemonium with the insouciance needed to do their jobs, but is sadly like a 12-hour episode of Supernanny :(