system
A chat on subreddit /r/NoStupidQuestions
human
It's just an expression, but I've always read it as either "two kids and mom's pregnant with the third" or "either two or three children," the amount that was typically considered "average and normal" in a WASP nuclear family.
gpt
&gt;two or three children

It's more this, playing off the fact that the average was 2.5 kids per family.