How do terminate all child processes of a process?

[Marshall, Simon]

Hi, I've a feeling this is a dumb question, but here goes and I hope
someone can help...

I have a script (call it A) that sets off background processes and
dutifully waits for them.  Each background process is another script
(call it B) that sets off a foreground process (a binary executable in
this case, call it C).  I want to be able to ^C (or whatever) script A
and cause scripts B and binaries C to terminate.

Here's how I naively think it should be done: A sets a trap and kills
Bs' pids.  Unfortunately, it doesn't work.  Bs gets killed.  However, Cs
are not killed.  Here's a simplified test case to illustrate it:

#!/bin/bash
# Script A
cmd="B 60"
exec $cmd &     # Use exec to avoid an intermediate shell.
pid=$!
trap "echo $pid; kill $pid; exit 1" HUP INT QUIT TERM
wait $pid
status=$?

#!/bin/bash
# Script B
cmd="sleep $1"
eval $cmd

Here's it in action:

With A running: ps -fu marshals
UID        PID  PPID  C STIME TTY          TIME CMD
marshals  9954  9953  0 09:39 pts/2    00:00:00 -bash
marshals 10033  9954  0 09:41 pts/2    00:00:21 emacs
marshals 11415  9954  0 11:12 pts/2    00:00:00 /bin/bash ./A
marshals 11416 11415  0 11:12 pts/2    00:00:00 /bin/bash
/home/marshals/perth/c
marshals 11417 11416  0 11:12 pts/2    00:00:00 sleep 60

Now interrupt A, which outputs 11416 from the trap: ps -fu marshals
UID        PID  PPID  C STIME TTY          TIME CMD
marshals  9954  9953  0 09:39 pts/2    00:00:00 -bash
marshals 10033  9954  0 09:41 pts/2    00:00:21 emacs
marshals 11417     1  0 11:12 pts/2    00:00:00 sleep 60

See how 11416 (the shell running script B) has indeed been killed.
Unfortunately, it has not killed B's child process, the sleep process.

How can I arrange for all processes started by A or A's children, etc.,
to be killed when A is interrupted?  Note that I also want to get the
exit status of B.

Many thanks in advance, Simon.