The issue is that kids that grew up without a healthy approach to food become the very parents that perpetuate the behaviour; they just don't know any better because they haven't been exposed to good eating habits, either at home, on the tv or at school.
It's a social thing. The parents are clearly responsible for educating their kids, but as a society we shouldn't think it's OK to advertise and serve dangerous crap to kids and just assume that this doesn't affect behaviour (the very purpose of advertisement is that it affect people's behaviour, I always found it strange that we then blame them for being influenced).
You have to start very early to educate kids senses to appreciate flavours more subtle than fat, salt and sugar.
When Jamie Oliver attempted to change the horrendous 'meals' served to kids in the UK, he hit this very issue: lots of kids preferred to eat their crisps and junk food rather than the balanced, healthy and tasty meals prepared for them by a top chef (meals that didn't cost more than the crap they were usually served).
Contrast that to the meals served in schools in France: they are balanced, varied, there is always some choice. You will always find a choice of starter, main course, cheese/yoghurt and dessert. These kids find it normal to eat their vegetables.
Parents wouldn't have it otherwise.
In France at home, most people actually cook. Everyone orders pizza once in a while, but the vast majority of meals are actually cooked from fresh. It's not a money thing: you can get cheap produces. It's a cultural thing: cooking is fun, it's a skill people pass down the generations, it's time well spent, it's something to be proud of, it's a part of normal life.