This cheese knife is awesome:

http://www.amazon.com/Fairchild-OKT-The-Cheese-Knife/dp/B000FA00YG

a) It's a really great cheese knife.
b) It's also the exact shape, heft, and function of a chef's knife, for preschool-size hands.
c) It's sharp enough to chop real food, but it's plastic, so it's not going to chop little fingers.

DS learned to chop carrots, celery, etc. with it sometime between 3 and 4. He loves cooking.

Ours just developed a nick in it after about 3 years of use. I'll be getting another one.

I give my 4 year old a paring knife. The 2 year old uses a butter knife.

Anonymous wrote:This is counterintuitive, but the knife should be small enough for the kid's hand and very sharp. A dull or safety knife can slip and cut them. You are less likely to be cut with a sharp knife held carefully and used slowly.

Depends what you're cutting. I like to start very young kids with things like bananas and watermelon and cutting cookie dough into shapes with a butter knife. Once I know they're positioning their hands in the right way, and are moving slowly, then moving to a sharper knife and stuff with more resistance makes sense. I agree that sawing at something with a too dull knife is a safety hazard.

This is counterintuitive, but the knife should be small enough for the kid's hand and very sharp. A dull or safety knife can slip and cut them. You are less likely to be cut with a sharp knife held carefully and used slowly.

A medium sized sharp knife works. I have a wusthof "sandwich" or utility knife that my kids and now my grandkids use. Teach them how to use it and supervise.

can use scissors to cut green onions

I let my 3 to use a butter knife.

Pampered chef has a kids safety knife. It's kinda like those pumpkin carving ones but much less serrated.

Not a knife, but my kids have both used this device with success:

http://www.forsmallhands.com/vegetable-chopper-with-wooden-handle?utm_source=googleprod&utm_medium=web&utm_campaign=GoogleProductSearch&utm_content=D325&gclid=CJC7kfDU_roCFU7xOgodOEAA0w

Title says it all...