Who said it was that simplistic?
I clearly stated in what you quoted that it was NOT a simple process. Actually it is a rather complex and nuanced process. Movies and TV shows are part of our environment and as such have an impact as we learn about new things, ways of being, make sense of the world. No where did I say it was the ONLY influence in a child's life. Of course it isn't. But it IS part of the world for many children and as such has an impact in their socialization. Again not the only influence, probably not the most important influence (you are correct, family plays a much larger role in the younger ages but that does start to diminish as children get older), but it IS an influence.
Just to give you a sample of what TV and movies have been found to influence: acceptability of violence, perception that the world is a more violent place than it actually is, aggression, gender role ideology, future expectations, acceptance of stereotypes, body image, self-esteem, and sexual attitudes. These are only a small sample of connections that have been studied and found to exist. Does it necessarily mean that watching one movie will make you think you can fly or make you even murder someone? Of course not. We're not that simplistic. But can watching similar portrayals over and over again color our perceptions of the world, especially things we perceive as possible? Yes it can and it does according to the evidence. No, it doesn't mean an older child (pre-schoolers might) believes in magic carpet rides, but it means they may be paying attention to the way Jasmine and Aladdin interact and relate to one another and file that away as part of other information they have about romantic relationships. Notice it's not the ONLY information. Just part of that information.
Of course it all depends on what they're watching and what the messages/portrayals are. The more consistent the message the more impact it has. Heck episodes of Sesame St. have been found to lower gendered stereotypes and increase acceptability of minorities. So these media portrayals can have positive influence. This is why it's useful to critically think through the portrayals in the media. Yes, those princesses can be passive, but then we have Mulan, a strong character who saves her country. What an awesome role model for little girls who are trying to make sense of what it means to be a girl in our society.
But again media are only one of many voices in a child's life. This is why I said, my children watch these movies, but we also talk about what happens in them, what's realistic and what isn't.
) has made them very secondary to male characters, and often has their flaws or troubles ended because she finally has her man. Not exactly a feminists dream.
there's always one 
