John Calvin Commentary Exodus 21:31

"Whether it have gored a son, or have gored a daughter, according to this judgment shall it be done unto him." — Exodus 21:31 (ASV)

Whether he have gored a son. I do not know whether those who refer this to age are correct, as if the words 'son' and 'daughter' were meant to signify any young persons of either sex; but I do not reject this opinion. Still, Moses seems to extend the law, as if, in the event that a butting ox had killed its owner’s son, the father himself should be subject to the punishment for not having taken more care of his children. It might, however, be doubted whether it would be just to condemn to death a father already weighed down by the loss of his child; still, it provides a useful example, that parents should not escape with impunity if their sons or daughters should die by their fault.