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 f***ers.

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

David: Oh, theyre the animals that give us milk

Wife: but who said they were called, er, f***ers?

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