The problem is that it is a free country and we are allowed to eat as we please. Yes it's unhealthy but that decision should lie with the people demanding it of McDonalds and not wanting to make a law about it. If enough parents wrote angry letters or boycotted McDonalds to make those changes, it would change. The enforcement of it should not lie with the government to make laws but in the negative reaction of the people who buy the products. That is how free market works. It should be consumer driven.
As an interesting tangent, what is your take on (I really can't think of the proper way to phrase this) under-18s being deemed unable to make fully informed and responsible decisions? Would you have children tried for crimes in an advlt court, or do you take the same position as I do, that juveniles have diminished responsibility? I look on the food issue as an extension for this - children, especially those young enough to be taken in by a toy in a Happy Meal, can not be expected to make an informed and balanced decision. Thus, I'm sure we all agree, responsibility falls on the parent to look after their children.
Now, human life is something I place extremely high value on. "Life's too short to make another's shorter". The affects of eating unhealthy food are well documented, so I strongly believe that, if parents do not show due concern for the health of their children, it is the place of others in society to step in. "You can't tell me how to raise my kids" is a viewpoint I couldn't disagree with more.
So what if I want to eat a sloppy greasy burger!!?! Soon, the goverment will ban my video games!
You want to eat a sloppy, greasy burger? Eat one then. No one's stopping you. A similar approach already exists in video games - age ratings.
They are prohibiting the sale of Happy Meals. That means that McDonalds cannot sell them and people cannot buy them unless McDonalds complies with an unnecessary regulation that the governing body does not have the legal authority to impose. They are not "criminalizing" them, they are making them completely disappear from the market.
But they're not? McDonalds can still sell Happy Meals, there's nothing stopping that sale.
EDIT: With regards to the governance of San Francisco, I can't claim to have any knowledge of how it works. If there was to be a referendum on EVERYTHING though, nothing would get done. Only Switzerland has a referendum on everything.