First of all, think safety. Any child that has to stand on a stool or chair in order to reach the stove is too young to cook. Start younger children off by letting them help set and clear the table, gathering ingredients, and stirring, mixing or adding ingredients.
Next, set rules about handling knives and other sharp instruments and handling hot pans or boiling ingredients. Some parents start teaching their children to cook by showing them how to make things that don't require cooking first, and then graduating to letting them make food in the microwave.
Create a relaxed atmosphere that is fun when teaching your kids to cook. Remember what it was like when you were learning to cook? Chances are, you made a few messes and broke a few dishes. It happens. Learning to cook should be fun, not drudgery, although there are certain responsibilities that go along with the privilege, such as cleaning up as you go along, and leaving the kitchen clean when you're finished.
Start with the basics. Show your kids what the different utensils are used for, and the right way to use them. Teach them about herbs and spices, and using the right ingredients for the right dishes. Cooking is a great way to learn fractions and chemistry, and your kids might not even realize they're learning while they're having fun!
Begin with simple recipes. There are some great cookbooks for kids on the market today that include step-by-step instructions and pictures so kids can see what something's supposed to look like while they're assembling the recipe...let success build on success.
Give your kids a chance to shine. As they learn to cook more complicated recipes, let them be responsible for planning -- and cooking lunch or dinner one night. Letting your kids plan the meal -- and even shop for the ingredients will help them to realize and appreciate the effort that goes into cooking.
As your kids become more skilled, begin including foods from different cultures. Many recipes such as French crepes or Italian lasagna are not difficult to make, and your kids will develop an appreciation for many different kinds of food.
Especially for younger children, having tools that are their own size not only make cooking more fun, but make it easier for them to participate. Kid-sized kitchen utensils can be found at many department or specialty stores.
Make sure you take plenty of pictures -- you may not realize it now, but you're making memories that someday will be as delicious as that batch of chocolate chip cookies you're baking now!