the gnome-3.16.x desktop is available in the corepure64 repo.
gnome-session is used to start the desktop, but be aware that this is likely to pull in +/-250 additional extensions, depending on how many you have to start with.
Maybe you could start with the above and, if that's not to your son's liking, attempt to build cinnamon starting from the existing extensions in the corepure64 repo?