At that age the distro probably does not matter all that much. If whatever you choose doesn't work too well, you can install something else together. And cheer

At that age the distro probably does not matter all that much. If whatever you choose doesn't work too well, you can install something else together. And cheer at the new selection of wallpapers during or after installation. But since mimicking dad's work is important, try to make it look & behave somewhat similar to your computer :) (My sons used OpenBSD from ages two to four or five---I don't think they even realized that it was there, or what it was. They were more intent on playing gcompris, watching cartoons by way of a helper script I put on the desktop and experimenting with whatever piqued their interest at the moment.)