Child process in another group gets <defunct> after handling a signal - c

Question

I have got a problem with dealing with some signals. I have got child processes with different group ID than a parent, and those kids are dealing with SIGALRM which parent is sending to them. Sometimes it works good, but sometimes it is called only once, and a child is becoming . Do you know where my mistake could be?
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <signal.h>
#include <time.h>
int workers=2;
void sigalrm_handler(int signum)
{
printf("caught\n");
}
int main(int argc, char** argv) {
//region variables
char message[255]="Hello world!";
struct timespec sendSleep = {1,0};
struct sigaction new_a;
int pid;
for(int i=0; i<workers;i++)
{
pid=fork();
if(pid==0)
{
break;
}
}
if(pid==0)
{
//region sigalrm_handler
new_a.sa_handler = sigalrm_handler;
sigaction(SIGALRM, &new_a, NULL);
//endregion
while(1)
{
}
}
else
{
//region sigalrm_handler
new_a.sa_handler = SIG_IGN;
sigaction(SIGALRM, &new_a, NULL);
//endregion
nanosleep(&sendSleep,NULL);
for(int i=0; i<strlen(message); i++)
{
killpg(getpgrp(),SIGALRM);
printf("signal sent\n");
nanosleep(&sendSleep,NULL);
}
}
}
It is necessary to run it few times to get:
signal sent
signal caught
signal sent
signal sent
signal sent