My DS10 is working on the EPGY math courses. After he finishes them, he is interested in starting the EPGY computer science classes (Introduction to C Programming, etc.,). Has anyone's children taken the EPGY computer science classes, and are they appropriate for pre-secondary level students? When we applied to EPGY, Stanford informed us that he was pre-qualified to take the computer science courses--but we really do not know.

Alternatively, can anyone recommend other computer science programs that would be appropriate?

Depending on your son's computing/programming experience, take a look at the Alice Project from Carnegie Mellon:
http://www.alice.org/

Python, perhaps through an AOPS course http://www.artofproblemsolving.com/Wiki/index.php/Getting_Started_With_Python_Programming .

Scratch, as discussed in a thread here "Computer science book recommendations?"
http://giftedissues.davidsongifted..../all/Computer_science_book_recommen.html

Johns Hopkins CTY http://cty.jhu.edu/ctyonline/stemcourses.html#Compscitech has the courses

Scratch Programming
Introduction to Web Design
JavaScript
Computer Security Fundamentals
Introduction to Java
Advanced Java Programming

I do not recommend teaching someone to program starting with C. There are much more modern, powerful, and convenient languages available.

The languages described above can be installed for free. Many people can teach themselves to program just by experimenting with a computer language and reading online help and some books.