Terminate an NSTask and its children

I'm using NSTask to execute a series of long running commands like so:

commandToRun = @"command 1;command2";
NSArray *arguments = [NSArray arrayWithObjects:
                      @"-c",
                      commandToRun,
                      nil];
self.task = [[NSTask alloc] init];
[self.task setLaunchPath: @"/bin/sh"];
[self.task setArguments: arguments];
[self.task launch];

This creates a process for the shell, and a child process for whichever command is running at the time (command 1 or command 2). If I kill the task with [self.task terminate] it only kills the parent process. Is there a way to identify and kill the children too?