The Two Kids

So I told them off. Then their mother came over to me and said "Leave them the fuck alone! They're my fucking kids!"
Trying to think of a witty comeback, I asked her "Are they twins?"

She replied, "Of course they're not twins you fucking idiot, one is seven and the other is twelve! How could you possibly think they were twins?!"

I replied, "Well, I couldn't imagine anyone fucking you twice."