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).

Isn't that already on the tax return? Your dependent count would increment from the prior year. The IRS can also distinguish births vs adoptions and step children by the checking for novel SSNs.

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.