Small children should never use real knives. Instead, they can use plastic serrated knives, kitchen shears, spoons and even melon-ballers.
Plastic knives work well for tasks like spreading peanut butter or cream cheese for snacks. Kitchen shears can be used for everything from chopping herbs to cutting hot dogs. And spoons and melon-ballers can be used for cutting fruit, scraping seeds out of cucumbers and even peeling ginger.
Older children should learn to use knives properly. Knives should be sharp; dull knives can lead to accidents. And children should learn to hold knives properly with the fingers of their dominant hand securely gripping the knife handle and the fingers of their other hand curled under as they hold the food. Curling the fingers under ensures they don't get chopped off!
Remember, graters, zesters, microplanes and peelers are sharp, too. Children should not use these utensils until they are old enough (usually around age 9 or 10) to learn to use them properly. And no matter how old your child is or how adept he seems to be at cooking, you should always be there in the kitchen with him when he's cooking.