Kill all the children

1.sh

#!/bin/sh
echo outer
./2.sh
echo /outer

2.sh

#!/bin/sh
set -e
#trap 'ps -opid= --sort=start_time --ppid=$$ | head -n-2 | xargs kill' INT TERM QUIT EXIT
kill_children ()
{
    PPID=$1
    for CHILD_PID in $( ps -opid= --sort=start_time --ppid=$PPID | head -n-1 )
    do
        kill_children ${CHILD_PID}
        kill ${CHILD_PID}
    done
}
trap 'kill_children $$' INT TERM QUIT EXIT

echo inner
sh -c 'sleep 0.6 ; echo -n ~~~' &
sh -c 'sleep 0.5 ; echo -n HELLO' &
echo /inner