Mishnayos Brachos Perek 7 Mishnah 2

וקטנים אין מזמנין עליהם – Especially small children who do not know to Whom they are reciting a blessing (ברכת המזון ) a minor who knows to Whom He is reciting a blessing, they may invite him to join [in the group recitation of ברכת המזון], and there is something remarkable that says that we are not speaking about a minor who knows to Whom they are reciting the blessing that we invite him to join [in the group recitation of ברכת המזון] but rather with a child who is thirteen years of age plus one day, who has not brought forth two pubic hairs (which demonstrate his having attained adulthood), and he is called a “blossoming minor” but younger than this, we do not invite him to join [in the group recitation of ברכת המזון] , even if he knows to Whom we are reciting this blessing. And in the Jerusalem Talmud, they bring the Practical Halakha, that we don’t invite the Minor at all, until he grows up and brings forth two pubic hairs. And women invite other [women] to recite ברכת המזון as a group for themselves and slaves invite other [slaves] to recite ברכת המזוןas a group for themselves., but women are not [invited] with slaves because of licentiousness [that would ensue].