The other day I was at work and my wife had an appointment. My in-laws came over to watch the kids. My wife had a list of instructions for each child to make it easier for her parents. What to do for naptime, snacks and activities.
Snacks for oldest, she listed, Apples, plums or carrots and for the other, apples or carrots. Both kids enjoyed an apple while watching a video during naptime for the baby. They were not offered chips, cookies, or cakes. They didn't even think to ask. We don't have it at the house and they know they only get it during special occaision or if they are at their grandparents.
Now as I have mentioned before, to have your kids eat healthy, first thing you need to do is model. The kids always see us snacking on fruits and when I make my lunch, they see the vegetables I take. I never take junk.
They know we save sweets for special occasions. In fact this past weekend, we made ice cream sundaes to celebrate a birthday. They got ice cream, chocolate chips and cookies to go on top. Kids want to be like Mommy and Daddy including their eating habits.