I have very clear memories of watching chickens run around with their heads cut off---the old axe on the stump and let er flap method. I thought is was THE funniest thing I'd ever seen---I had to have been less than five. Maybe a slightly morbid kid
One of my mom's favorite stories......
We raised a steer, Toro, and butchered him. We'd known he was for meat, but I know my older sister rode him at some time
Anyway.........we sat down to dinner and I asked if we were eating Toro. My mom took a deep breath and replied we were, indeed, eating Toro. I forked a bite and said " He sure was a good ol' cow, wasn't he?"
Again, probably four years old. Morbid, morbid kid.
Littles don't know they're "supposed" to be wigged out by butchering animals. Just let them know from the start the cute chicks are to eat, and guard your OWN emotions, that's what will guide your kids, is your own feelings and response.
Good luck!