Rashi on Exodus 21:31/רש"י על שמות כ״א:ל״א

1או בן ינח WHETHER HE HAVE THRUST A SON — a son who is a minor;

2או בת יגח OR HAVE THRUST A DAUGHTER, who is a minor. Since it states, (v. 29) “and hath put to death a man or a woman”, one might think that the owner is liable only for the death of adult persons, Scripture therefore states, “whether he have thrust a son etc.” to make him liable for the death of minors equally as for that of adults (Mekhilta).