I think fast food companies should be allowed to advertise, like any other business. However, I propose the following restrictions because of the high number of ads aimed at kids:
1) No targeting of children in fast food ads.
2) No sponsorship of cartoons and "kid's clubs".
3) No bundling of toys and a kid-related products with fast food.
4) No setting up of playgrounds or "daycare" centres at fast food locations.
This would be for the same reason we don't allow cigarette ads to be targeted at kids: Children are not knowledgeable enough to make health decisions.