Since there is not enough info here, I am making some guesses. Your son was probably using an squashfs based system. squashfs is a compressed file system used when there is a disk space crunch. Now there are two chances
1. squashfs folder(?) contained the root(?) file system
2. It was the mount point
In the first case, you are almost lost. In the second case, you can just try creating the folder again using the mkdir command. One solution that might always work is to copy this folder/file from another similar computer to the location from where he deleted it. (You can download a bootable USB image and use that for rescue)
Did a bit of search and found this http://isohunt.com/torrent_details/5...tu?tab=summary
. This might be useful to you.