You are misunderstanding the importance of the toy. Following the meal with a toy reinforces the behavior so that in similar circumstances in the future the child is more likely to repeat the behavior in expectation of the reinforcer (not the food). Desiring the happy meal has less to do with a kid wanting the happy meal versus the kid wanting the toy. And a toy is a pretty strong reinforcer for a child.

The best part of it all is that the process of reinforcement doesn't even have to be conscious, it doesn't have to be thought out in terms of expecting a reward. Truly, most reinforcement and learning is not a conscious act at all. This is Behaviorism and Learning Theory 101. The companies didn't just pull the idea of a kid's meal out of their asses, they planned it with a complete understanding of how learning and behavior work.

By the way, what do you think things like Monopoly or rewards programs are? They are reinforcers for adults and boy do they work. McDonalds cashes in on repeat business every time they run their Monopoly contest as people pile in to get their stickers (not eat because they are hungry).

That isn't to say that I think the government should legislate happy meals. I still think it is the parent or parents' responsibility to monitor the behavior of their child(ren) but don't just poo poo this as ridiculous. The toy is definitely a well planned out psychological manipulation that the companies know full well they are doing. If I were to support the government doing anything though I would support them sending a pamphlet to their citizens explaining how they're being hoodwinked by companies who want to sell them really bad food until they croak from disease and can't buy it anymore.