Child process can be created by POSIX function fork(), and below is the demo code.

pid = fork();

if (pid == 0) {
    /* processing of child process */
} else if (pid < 0) {
    /* parent process: handle errors */
    perror("fork");
    exit(-1);
} else {
   /* parent process: the parameter of pid is the ID of forked child process */
}

And also, parent process could call function wait() to wait for finish of child process, instead of processing in the second return of function fork().