I think the Opinel #6 is the perfect knife for a young kid. It's a friction folder and not a spring based slip joint. This means that there is no spring trying to move the blade when opening and closing. It comes with a lock ring, so it can be locked open. Opinels are also very inexpensive, so if lost, easily replaced without breaking the bank. They're a little on the crude side out of the box. Many people sand down the inner surface of the pivot area (fold sandpaper over a spackling spatula) to get them to open easier.
I started my kid with an Opinel and would do the same again. Took him several years to have the hand strength to open and close slip joints safely.