I've a few points to make. Firstly, most of what moviebob said was a fair argument (though the opening was bordering close to eugenics), though this issue of childhood obesity is a major one.
As a british medical student, part of our training revolves around public health, and naturally we did work on childhood obesity. Undoubtedly it is a serious problem, arguable more-so than smoking now. The morbidity can be just as severe (everything from type II diabetes, heart failure, stroke through to increased risk of certain cancers and complications under anaesthetic for surgery) and the sheer prevalence of it now - in the UK over 25% of children will be obese by 2050 - and that fat children often make fat adults - makes my point. The cost of this is already £16 billion annually, set to rise to over £50 billion by 2050.
Now its not all due to diet, we can't just blame corporations, and the parents need to be held accountable. But on the other hand, parenting is very difficult, and if a child tells mummy he wants McDonald's, sometimes for mummy its easier just to let her son have what he wants instead of dealing with the consequences. As for your options given in you video - interfere with the parents, or interfere with a corporation, I know what I'd back, and it isn't with you. Child protection courts in England are already shrouded in controversy and trials held behind closed doors, with numerous examples of children being taken away (okay, a lot of the time justifiably). I would suggest that you yourself don't have enough experience in the matter to judge that parents of overweight children should have to defend themselves from a government. So a more practical approach with fewer ethical issues would be to prevent such fast food companies from targeting children in the first place, so that a generation will hopefully grow up healthier and pass the lifestyle to the next. For as you said, if targeting junk food doesn't solve this epidemic, then how long before video games get brought into it?
I hope you (moviebob) read this (as you mentioned in your recent column), as I believe these arguments important and you have a voice more likely to be heard than mine.