Obese children are more common in Britain than e.g. in Sweden.
Various reasons for this:
Different working culture, less work presenteeism and more acceptance of workers needing to get off work on time means more time and energy for parents to cook.
Different food culture. Jam sandwiches and crisps are NOT regarded as a meal option in Sweden. Crisps are party food only, giving them to a child on a daily basis would be regarded as close to child abuse.
Sweet drinks, again, are seen as something you serve at parties or with snacks, not for lunch or dinner, unless (I suppose) there are genuine SN needs. Children get used to drinking milk and water from a very early age and don't expect to have coke for everyday.
The fact that all school meals are free means it is easier for schools to stick to a healthy diet and ignore children's preference for fatty and salty foods: very few parents are going to want to pay extra money just for the privilege of feeding their children junk food.
Children start to learn preparing food in nursery and there is a cultural expectation that cooking at home is just something you do.
As far as I am aware, cookery lessons are still adequately resourced and timetabled and very much about learning techniques rather than fancy presentation: they certainly were in my day. All the Swedish children I know know how to cook.
There is much better access to the outdoors, partly for geographical reasons, but partly because parents genuinely believe that it is unhealthy to stay cooped up even if the weather is bad. They prioritise good outdoor wear before many other expenses because it seen as a must-have. Nurseries help here too, as they have a policy of taking children out to splash in puddles or roll in the snow.