I can't speak for French children, only English and Spanish, as those are the countries I've lived in and taught in. In Spain, Italy, France etc, the big difference is that life is centred around family time. There as much compartmentalising adult time, child time and family time, like in the U.K. Kids stay up later, go out with family and although adults do go out alone, more often than not the kids go out with them. Also, for many people, they live closer to their family and weekends are spent in a more simple way having a meal together in a restaurant or just spending time at home. There isn't the emphasis on kids doing so many activities to keep them occupied. In Spain certainly, expensive days out or child centred activities are usually replaced with walks together, trips to the beach, visiting grandparents etc. Of course they play football and do activities too, but not to the extent kids in the U.K. do.
The Spanish language and culture is much more direct, louder and less confined by social etiquette and politeness than U.K. culture, so it's accepted for kids to be loud, boisterous etc, in a way it wouldn't be in the U.K. Families mostly to go restaurants where kids can run around a outside, and they certainly don't sit like French children apparently do, not are they expected to.
The teachers in schools, certainly in the area of Spain I live in, have a very hard time as there is a lot of low level bad behaviour - talking when the teacher is talking, getting up in class, shouting out etc - this is very different from what I experienced in the U.K. as it was only a few children who did this, here it can be almost the whole class. The older teachers are often shouty, angry and stressed from years of it and the younger ones are completely overwhelmed.
I think English kids have been given a bit of a bad time on this thread, as I actually notice how polite they are when I visit the U.K. There's an expectation to say please and thank you and be generally well- behaved that there isn't in Spain. That's comparing apples with oranges though as the culture and expectations of how children should be are very different in both countries. Children have more freedom to be children in Spain, which may seem to a Brit as unruly behaviour, but it wouldn't be perceived in the same way here. I don't really think people should compare their children to children from other countries as we're all differently societally and culturally as adults, as are our children.