Is it only if the child is the MOTHER’s firstborn son? What if a woman marries (a second marriage)someone who never had children, and they have a son. The child is HIS firstborn male. Does he require a pidyon (I know it is bechor peter rechem that requires it, but does that expression mean for just the FIRST husband)?
I could see the sperm donor (if non-Jewish) being a potential shailah, but the MOTHER is Jewish, so her child is, too, and all Jewish children are chayav in the same halachos.