OK, first thing is the NVDA screen-reader from NVDA-project.org. Assuming they don't already have screen readers on the computers, that'll let them use the computer for anything from coding to email.

Second, for a starter programming language, I recommend a language called BGT. It's made entirely for building audio games, so comes with functions to make sounds, pan, etc, built in. It's also now completely free. It's based on angel script, so has a standard C like syntax; if you're familiar with Lua, JavaScript, or any similar scripting language, you should be able to pick up BGT in about a day. Yes, it is extremely simple, but it's a good place to start teaching concepts, and get a program they can compile and run that actually does something within an hour or two. Get it at: http://www.blastbay.com/bgt.php