This project was a blast and my little guy loved it. The whole process is very simple and little hands struggling with dexterity can help with a lot. I had an idea in my head of what I wanted but he got to make most of the decisions about wood selection. My advice, encourage your little guy to make all the choices he or she can and as long as it has no effect on the functionality use them. He is still proud when they get taken out and used and they have held up well.
On your wood selection I recommend sticking with woods that grow things humans eat for the most part. A nice bland wood like maple, birch or cherry (as I used here) will not impart a taste to the food. Some people can be allergic to black walnut and oak can leave a flavor. I would avoid pine, fir or larch and ALL mystery woods. Ceder would work well and would be gentle on your knives but it will show it's use more than others.