From a very young age, the media teaches children how to be consumers in society. The media tells children about everything from what types of cereal to eat to what type of clothes to wear. They do this by using a creative technique that doesn't involve selling the product itself.
Commercials aimed towards children (and pretty much everyone else also) don't sell products at all. Instead, commercials aim to sell an emotional response in regards to their products.
For example, advertisers don't sell hamburgers, fries, and a drink to children by telling them the food is good for them, or that it's cheap. Instead, they're selling the idea that eating this food will somehow cause an emotional response in them. For example, if the other kids at school eat at this fast food restaurant, going to another fast food restaurant (with a different image) will garner a different response at school.
Another example is when selling cereal to children. Advertisers focus on using the character on the cereal box as a way to get children to recognize and pick up the box the next time they visit the supermarket. The advertiser isn't selling the taste of the cereal (except for saying "it's yummy!"), and they certainly aren't selling the fact that these cereal are filled with sugar. They're selling the emotional response associated with their view of the cereal.
This affects children deeply, as children are taught to base their purchases on emotional desires rather than actual need. One such desire is the need to be liked. Children often want to buy products that make them seem cool in the eyes of their peers. If one child wears designer jeans, and those designer jeans are seen as the thing to wear to be cool, other kids will want to wear those same jeans.
Another one of emotional selling's effect on children is that children are taught to like or dislike something based on the emotions planted by the advertisers. When combined with societal views from other people, children create views of what's good and what's bad. When selling toys for girls, advertisers write the commercials to have an emotional response with girls. If boys dare have an emotional response to these commercials, they're ridiculed by classmates. This creates a divide between the boys and girls in the classroom, and in society in general.
As children grow older, advertisers already know that they have been conditioned to react emotionally when a certain item is presented. When they're children, the emotional response is for breakfast cereal or toys, and as they age that response shifts to make-up or sports, and later on to electronics and cars.
Once gender and societal roles have been pre-defined as children, advertisers have an easy time selling products using these roles when the children become adults. And when advertisers find it easy to sell unneeded products to adults, they've certainly created an effective, but passive, consumer.