Pretty dumb law, IMO.
I agree with Supervisor Gage in that if you can't reign in your kids when they want a happy meal/toy, you are in for a world of hurt as they get bigger.
I'm not crazy about McD's, but I do let my boys go once in a while. They share a happy meal, and enjoy playing with the cheap toy for a long time.
You have to use some common sense as far as how much, if any, fast food to let your kids eat, based on their body types, metabolism, etc.
My 7 yr old is 42 pounds soaking wet. Empirically, it doesn't seem like half of a small fries & some chicken nuggets every couple of weeks is enough to blimp him out. Likewise for his kid brother. Of course, they get plenty of exercise and usually eat pretty healthy stuff, so YMMV.