Have you filled out a federal income tax return in the US?

It absolutely asks for the names (and SSN) of any dependents. It's trivial to infer whether one of the adult(s) filing the tax return gave birth in the last 12 months based on the last 2 years of tax returns for those adult(s).

My home country pays a baby bonus to people and it's administered via the tax system, so I think we ask something very similar actually.