Since new processes all belong to the same process group, that of the parent process, have a process start a bunch of processes (`fork`), and then with appropriate logging and a delay, type `Ctrl`+`C`. They all eat a `SIGINT`.
$ perl -E 'fork for 1..2;say "ima $$"; $SIG{INT}=sub{die "woe $$\
"}; sleep 999'
ima 80920
ima 80922
ima 80921
ima 80923
^Cwoe 80920
woe 80922
woe 80921
woe 80923
$
(Add `strace` or `sysdig` or such to see the system calls or signals involved.)