How to understand child died because of memory from parent even the signal send is "9"

How to understand child died because of memory from parent even the signal
send is "9"

My project which runs 10 child processes has some memory leak,and it is
sometimes running out of memory.
Parent process respawns child processes if they died with operating system
signal for example signal 11. And does not respawns in case of signal 9
because , I may really need signal 9 to terminate processes(like prompting
killall -9 myproduct). .
The problem starts , when childs uses extreme memory operating
system(FreeBSD 8.3 in my case) send signal 9 to the child. But even it is
signal 9 I want to respawn the dead process because it is not triggered by
user.
Do you have any idea how can I seperate between the signal 9 caused
because memory problem and triggered by user. And is there any C tutorial
or example code which you can advice?