Kids mode was a suggestion I made ages ago. My kids age 6 and 7 have both now got the hang of using the tablet and picking colours and so on, but it was surprisingly tricky at first. I still need to help them out now and again.
An application lock and an easy way for them to save/create new images would be the most important suggestions. I'm not keen on them having access to a file dialog.
Perhaps an ArtRage journal type of thing would be better. Each user would have an easily selected profile which recorded their images in a calendar.
Another suggestion for the very young would be for ready made pencil or crayon sets. Perhaps ArtRage could get sponsorship from 'Crayola' for a free kids version.
See Crayola's flash drawing app.
ArtRage for Art | EnergyXT2 for Music | Blender for 3D