With a moo-moo here...

My wife is a primary school teacher, and related this tale after another class returned from a trip to a working farm:

My wife asked little David if he had enjoyed the trip.

"Yes it was great - we saw sheep, horses, goats, and fuckers."

Wife: "er, fine, fine. I know what the sheep and the rest are, but what is a fucker?"

David: "Oh, they're the animals that give us milk"

Wife: "but who said they were called, er, fuckers?"

David: "that was our teacher. Well actually she called them "effers", but we all knew what she meant."