Quoth Brandon Allbery
terminateProcess passes on the semantics of kill(2); on SVID-compliant (and I think POSIX.1-compliant) systems, the negative of the process group leader's process ID is used to signal the process group. Note that you may need to arrange for your initial child process to invoke setpgrp() to insure that the parent program is not part of the process group.
... and that stuff can be found in System.Posix.Process. Support for POSIX killpg can be found in System.Posix.Signals, by the way in case you think that would make your intention more transparent.
However I'm unclear as to the situation you are encountering, as your example does not appear to be spawning an intermediate process.
I missed that at first myself -- he actually invokes "time sleep 60". Donn