Define "isn't working". Do you get an error message? What do you expect your script to do that it isn't doing? What is it doing instead?

Off-hand, your script is forking and staying forked. Your system call will return when the command is completed, and then continue execution of your script just as if it were the parent (at least until the parent kills it). Have you verified that the script will successfully do a system call with that argument without problems?

I'm also tempted to ask you what you're trying to do here. Is your sleep/kill combo an attempt at enforcing a timeout? Consider alarm in the child process for that. Either way, you're going to be a lot better off putting an exit after your system call, or use exec instead of system (checking to be sure exec doesn't return in an error).

If this doesn't help you, we need more information.