It depends on your goal.
If your goal is to teach how to program an FRC robot in the least amount of time (in order to allow for testing of various components as well as driving practice), teach them LabVIEW. There are many free resources available as mentioned earlier in this thread. The teamrush27 programming guides are exceptional. See
http://www.teamrush27.net/rookie-resources
If your goal is just to teach programming skills, go ahead with either LabVIEW, C++ or Java, but expect to spend months on the Java/C++.
Contrary to popular belief, there ARE many technical programming jobs available using LabVIEW. (Search on labview job colorado since you are in Colorado.)