If you think about it, all real animals are cannibots, or descended from them.
The first bacteria were autotrophic (technically chemotrophic, but bear with me). Then some of them evolved to do eat other bacteria and still be autotrophic. Then some of them evolved to rely exclusively on autotrpohs for energy. They made no more themselves. Then some of those learned to eat other non-autotrophic bacteria, becoming omniverous. Then some specialized still further into carnivores.
So the reason that bots are evolving to be cannibots is because it's an open niche that can be exploited. There are even some real organisms that eat their own kids right off the bat. The trick is for kids to learn to run away. Run far away. Maybe have a gene that if the bot you're looking at is one of you, and has more body than you, and you're young, hit the .dn with avengence.
Also, maybe you should blind your parent.
cond
*.eye5 0 >
*.age 50 <
*.refbody *.body >
*.refeye *.myeye =
start
100 .dn store
-50 .shootval store 'or any other value that will make your parent not chase you.
.eye5 .shoot store
stop
Just an idea. I might make a cannibot with this and see what happens. You definately need to disable the birth tie for this to work well. Might work well with venom to blind the parent as well. I'm no sure if kids get a portion of the parents venom or not though (but you could always make alot first cycle).