I would have signed it, but I don't agree with this idea of hiding children from seeing people smoke. People smoke, people can smoke in most outdoor places and children will see this - seeing it doesn't make them automatically want to light up or any more likely to become smokers themselves.
I'm also not sure you including theme parks on your list. They aren't on the whole aimed at children, they are aimed at everyone.
For places like parks and childrens farms I agree it should be banned but I think we need to be careful not to alienate smokers.