In the past months, with the help of Casey, I wrote a library that tries to make it more convenient to run child processes from rust programs. It's called cradle. We've been using it for a couple of our projects with success. We've just released version 0.1.0. Which means that it's not feature complete, but we don't expect drastic API changes to the existing functionality.
If you try it out, please let me know what you think! Either here or in the issue tracker.