You don't say what sort of project you want. You can download the full set (40 !!) of the MagPi official magazine for free as PDFs from
https://www.raspberrypi.org/magpi/issues/ - your son (with your help if you want) can read those and select a project. I would probably start with Scratch programming
You don't say if you have got it set up. You might like to check this out before Christmas; like missing batteries, it might be a bit disappointing to open a present that he cannot use

- which starter kit is it? (yes, I know it 'should' just work!)