thumbElf sorry for the delay in replying to your question (have been working LOL)
It's very difficult for us as health professionals to get parents to realise there is a problem with their child's weight. I'm not talking about children that are a little heavy, or tall, with weight proportional to their height. I'm talking about children who are significantly overweight i.e. their weight is at least 2 centiles higher than their height.
We send a letter that is pretty blunt in my opinion, but then there's no beating about the bush. It basically says 'your child is overweight, here is a leaflet about healthy eating and exercise (NOT dieting! diet is a 4 letter word IMO!) and phone us on the above number if you want more info, advice or support'.
Virtually no parents respond. And many of those that do phone just to tell us to fuck off and butt out of their business, what their child does/weighs/looks like is up to them etc etc. (These are parents that have consented to screening by the way).
It is such a challenge. We work with the schools to promote healthy eating, exercise, self-esteem and self-respect, as well as advising on situations where a child's weight is impacting on their schooling eg they can't manage PE or can't join in games in the playground.
I really believe that parents are in denial, but it is perpetuated by society. We have this bizarre dichotomy in that adult females are expected to look like pre-pubescent children yet we expect even babies to be chubby. You rarely hear someone describe a slim baby as cute whereas chubby ones are often cooed over and told they look like a healthy baby, look at those chunky legs etc. Then we make constant excuses for overweight children - he's just solid/chunky/muscly, she'll grow out of it, it's just puppy fat, oh but I can't refuse her a treat etc.
Combine that with a lack of exercise, over reliance on cars/pushchairs, fear of letting children outside to just run around and you have a recipe for disaster. It's cheaper (and easier) to feed your kids crap from Iceland than to make them fresh healthy food with lots of fruit and veg. A whole generation has no idea how to cook a basic meal. Clothes are bigger. People think playing on a Wii Sport is exercise.
It's a socially complex problem and I don't think there are any easy answers. Education can only go so far.