For certain categories, the adult is definitely the customer. For toys aimed at children under three, the ads regularly talk about training hand-eye coordination and other basic skills.
For other categories, you could argue that the toy companies are selling a service: Make the kids stop complaining for a few hours. Naturally, an easy way to do this is to be the reason that the kids are complaining in the first place.
For other categories, you could argue that the toy companies are selling a service: Make the kids stop complaining for a few hours. Naturally, an easy way to do this is to be the reason that the kids are complaining in the first place.