-file permissions, users, and processes on Linux
-environmental variables
-package management
-common Linux packages such as X, top, and probably others
-piping/IO redirection
-what a daemon is
-possibly how to use a "real" editor such as emacs or vim
-possibly some shell scripting
More importantly, this kids will never be afraid on the command line (which I believe most people are, including younger programmers just learning how to interact with shells).
Many of the topics above show up in a computer organization class in a university. Computers are built on top of many abstractions, and the command line is at least one layer lower of an abstraction than a GUI.