While I personally feel fast food chains can all go choke on their "HCrappy Meal" toys, generally I think if someone wants to give something away for free, or charge for it, fine. Hell, let every kid get a free spent depleted uranium penetrator, as far as I care. They're only "mildly radioactive." The real question here is "Why would someone buy their kid one of these meals in the first place?"
I was raised by parents who tried to introduce me to a variety of foods. In that spirit, they might have fed me a Happy Meal on occasion — I don't ever remember getting one, though — but what I was generally expected to eat was what they were eating. At home, that meant what they were cooking (but I was sometimes allowed to skip a particular item: e.g., if they were making fried fish, slaw, cornbread, and potatoes, I'd be allowed to eat my fill of the cornbread, slaw, and potatoes, and skip the fish). If we went out, which wasn't a lot, I (after a certain age) ordered off the menu; I never remember seeing any sort of child's menu. If I committed some horrid sin, like ordering a tuna fish sandwich and a cup of hot chocolate for my birthday at a nice seafood restaurant (yes, this really happened), they might check, but I was allowed to hang myself under those circumstances.
So, why buy your kid this stuff? To distract them with the toy? Perhaps one could bring a toy or a book. Perhaps they're hoping not to be bothered by their kid while they're killing their Big Mac. I guess we'll see whether parents value being able to ignore their kid at a dime per kid or not. Personally, I imagine it'll fly: I can see mothers all over the Bay Area giving their kids dimes to put in some Ronald McDonald House "donation" box, the same way my mom used to give me dimes to stick in those March of Dimes collection boxes.
For my beloved City of San Francisco: Since you've already dived further into the regulatory waters of dictating meal content (as has the State of California with another ill-considered foie gras ban), why not regulate menus? Forbid the presentation of children's menus altogether. Or tax the presentation of a "child's menu," or that child meal itself. Remember, it's for the children. That phrase will get about anything passed.
When none of that works, chuck the whole mess into the water off Alcatraz. I hear about anything will drown off there.
Edit: "Wild Bears Shit in Woods," or it might as well say that. Who did The Atlantic et. al. think was paying for those burgers and buying those Happy Meals? And yes, most fast food places have a "dollar menu," but the same places are constantly testing the waters of newer, more upscale products they can still throw through a drive-through window quickly.