I just went through this decision and went with a 5" Kyocera petty/utility knife. I have very very curious and capable six and seven YO girls. They, like me cherish food and cooking and all love to work with their hands. The reason I went with these knives is because:
1.) Sharp, cuts like a real knife (steel knife) and is very forgiving on little fingers. Lets face it, learning to cut food with a claw hand does not seems intuitive, especially to children.
2.) The knife is light and handle fits well in small hands.
3.) The blade allows some push cutting and push/pull cutting. Mine littles want to push cut everything (I wonder why
Its not a real knife but it will teach them the things they should know:
1.) How to stand at the cutting board, hold the knife and where to put it when finished (thanks Eamon B. for your clear videos)
2. How to hold the food. Claw, hammer, finger point.
3.) How to move the knife, Up-down, Slicing or drawing.
I made a little sheath for ours. Ive had it for three months and its still relatively sharp. For $25 bucks on amazon. For the 6 to 8 YO child range it works.