First things first: Educate yourself about food and nutrition.
Don't make drastic changes. For instance, gradually decrease the fat content in your milk week by week.
Clean out the cupboard. Get rid of those chips and cookies.
Stock what you want your kids to eat and drink. Your kids won't eat vegetables? Try vegetable juices.
Get the kids into the kitchen. In the short term, they'll eat more fresh food, and in the long term, you're teaching them life skills.
Eat breakfast. It doesn't have to be elaborate: cold cereal, low-fat milk and juice make an easy breakfast.