"Good" and "bad" food is largely about perception. My wife did a test of that one time with a bunch of people were over. She made one of her casual smorgasboard feasts - adults and kids alike gobbing it down. Then she tacitly got the conversation going about vegetarians - for which the consensus was all negative about it.
Not one person realized the meal was entirely vegitarian, including the hotdogs, "sloppy joes," grilled brats and all the rest was entirely vegetarian. We're not vegetarian, though do limit red meat. Rather, the point is what is good food and bad food has a lot to do with how the food is prepared and presented. Telling kids "eat this because it's good for you" isn't the way to do it.