JessM's point about the underweight children in primary school struggling academically and reaching puberty later could well be linked to their emotional needs being neglected, along with poor/insufficient food.
Most of us will have had cereal/toast for breakfast, with full cream milk, jam and butter. Meat, poatoes and two veg followed by sponge cake and custard at school dinner, then another cooked meal at tea/supper time. In our family, if we asked for something between meals we were told to get a piece of fruit. A bag of crisps was a real treat and we had sweets on Saturday when grannie brought them. We ate a lot but we also had so much more freedom than most children do today. We ran about, rode bikes and generally played out a lot.
JessM's point about the difference in the weights of customers and their children in for example Waitrose and Asda is sadly correct. I've just seen on line, a report from a tv programme yesterday where a 22 stone mother complained that her obese 11 year old needed to go to fat camp. The mother complained there is no help for parents whose children are over weight, then went on to list her GP, a dietician, camhs, involvement with her daughter and how unhelpful that had all been. She said the government need to step in to help mothers like her.