Further reading then primary research

http://www.aber.ac.uk/media/Documents/short/toyads.html
http://www.aber.ac.uk/media/Students/lmg9312.html
http://www.aber.ac.uk/media/Students/lmg9307.html

After reading this and collecting, then analysing about four or five of them, (in terms of what you have read about gendered children's ads), you will need to construct your primary research with children. The obvious question is "are children aware of gender differences in advertising?" At 15, just how media literate and clued up about how gender difference is connoted are they?