re: If a person has one baby and one on the way

I think this may be more a connotation issue than anything.

For example, my personal pet peeve is someone who refers to themselves as a "single mother" when they are divorced and sharing custody.

Sure, technically they are single and a mother, but they aren't going it alone, which is the connotation (to me) of single mother.

So if someone tells me they have "two kids" I think of all the bullshite two kids requires. And there is a difference between two kids walking around and one not yet born when it comes to going about your day.