In principle a baby found on U.S. soil that you cannot find the parents of is assumed to be a baby born in the U.S. and therefore a U.S. citizen by birth according to the 14th amendment.

Anyone who thinks they are going to be sent to a concentration camp could ditch their baby at a fire station and I can't see how it wouldn't be a citizen.

You can't prove the child came from insert country unless you are taking blood samples from all the kids and populous and cross checking them to see if they match. It would cost way more than just ignoring it.

Mother's give home births all the time. And if people are anti abortion, then they better be ready for a lot of babies dropped off at fire stations without paperwork