Given the fact that most kids prefer fast foods and passive entertainment, what can be done to promote healthier lifestyles to young people

This is a literature site, but I can give you a general comment: I think incorporating a lot more outdoor education in the school system might be a way to get kids more active. Investing in ski, kayaking, hiking, camping ....and using cross-curricular methods to deliver education might be a way to medicate what you mentioned.