Many of the suggestions already made can be very helpful. Generally kids eat what is available, so by not having as much "junk food" around, a hungry child will try and typically eat the other "healthier foods" that are available. Careful not to create fights around food; rather than saying "you cannot have that food any more", state that "that food is gone, so here, try this instead". Certainly not having the foods in the home is an influence on what the kids will eat.
The 'rule of 15' still applies; keep offering healthy options to the kids. Eventually they learn to like many of these foods. Just don't force them to eat, but of course set an example by eating these yourselves.
The previous suggestions regarding a stable mealtime and especially getting the children involved in food preparation are very productive suggestions. The preschooler and Kindergardener involved in school or other (e.g., vegetable) food gardens often thrive and look forward to eating the foods they have grown and/or prepared in the kitchen.