My 7yr old Natalie, loves to go with me on outings on the weekend has learned to use one of my old Nikon FEs. I have also worked with the neighbor kids building pinholes and giving them disposable cameras that I reload with B&W. It is really wonderfull to see how children see the world through a camera. Natalie helps process the film and print.
She is not really interested in the bigger cameras because she wants to have the freedom to roam around and go through film. The best thing is she is learning to observe the world around her and appreciate subtle changes in light and color, how detail and form relate to each other and to take an interest in all kinds of natural and manmade objects and other artwork. If see continues to learn this but never uses a camera except for snaps it will be a great education.