killing a child process from pcntl_exec

Hi.. I fork a child process, using pcntl_exec. I see the process from the cmdline (using pgrep 123), but I can't seem to kill the pid from the cmdline, using "kill -9 123".. Is there something that I need to implement within the php test in order for the kill signal to be effective? If I wait, the child eventually dies.. but I'd like to be able to kill it from the cmdline. thoughts/pointers/comments... thanks