Getting kids in the kitchen
The first thing I would is get your kids in the kitchen. Get them to find a recipe to make and explain where all the ingredients come from. Getting your hands dirty in the kitchen is a great way to learn all about different food groups.
Getting them in the garden
Another great way to get your kids interested is to start a veggie garden. My kids really enjoyed the whole process, from choosing what vegetables they wanted to grow and having the responsibility watering them and watching them grow. They just love going up to the vegetable garden and picking what we need to go with dinner. I love seeing them in the yard just grabbing snow peas of the vine and eating them.