Your first ideas

Children and the Media
Do parents encourange their children to grow up too fast in relation to consumption of products?

The focus of your hypothsis, above, is not media, so we need to change it a little. How about looking at representations of childhood in the media, and the development of the "tweenager" first, then exploring parents' - anc children's - attitudes to it. You could focus on girls mags aimed at 8-12 year olds.

I like your insistence that it's happening for economic reasons and that this group has become a target market. I think it could be an excellent project.

You may find some relevant stuff in David Buckingham's After the Death of Childhood - the first chapter looks at how childhood has been constructed and represented. Also see what you can find here: http://www.aber.ac.uk/media/sections/advertising.html.

Primary reseach could be interviews with chidlren and parents about the images/representations you are exploring.

Sean