Especially advertising targeted at children. The way I see it, an advert is a business proposal and children do not have the autonomy to engage in a deal.
It used to be illegal to direct TV ads at kids in Sweden but it's now been legalized to harmonize with the TV channels that were broadcasting from the UK. Even though it's legal the networks have refrained from doing it as far as I'm aware. Not sure about other mediums though.
IANAL but my understanding is that wether an advert is a business proposal or not is based around the idea of an 'invitation to treat'[0] in contract law. It's pretty interesting reading about some of the cases where this concept developed.