Meaning of the expression "2.1 kids"

What does it mean to say, "Everyone in this city has 2.1 kids"? Is this an idiom?


Solution 1:

It means that the people in the city is stereotypically average-like, with a humorous twist.

Famililes in a region may have 2.1 kids by average. Saying that each familiy literally have 2.1 kids implies that they are average-like to absurdity.

Solution 2:

It's an ironic expression of an average as if it were an actual number.