We Never Know
No Slack
Fighting? Children aren't dumb, and why would you lie to them? What really are you protecting them from?
We're talking about farms, where such sights are pretty common and regular.
With your children did you play the santa, easter bunny and tooth fairy gane? Why lie to them? Kids aren't stupid.
But back on point. If two animals are having sex, young children don't know until they are told what's going on. The phrase "they are fighting" worked well when they were young.