The Gemora comments: This implies that he is not obligated in supporting his daughters, while he is obligated to support his sons. Additionally, it implies that there is no obligation to support one’s daughter but there is a mitzva to do so.
The Gemora asks: Who is the author of our Mishna? It does not seem to be Rabbi Meir, Rabbi Yehuda, or Rabbi Yochanan ben Berokah, as we shall see from the following Beraisa.
The Beraisa states that it is a mitzva to support girls, and certainly sons who learn Torah. These are the words of Rabbi Meir. Rabbi Yehuda says that it is a mitzva to support sons, and certainly daughters, as it is degrading for the girls. Rabbi Yochanan ben Beroka says that it is an obligation to support girls after the father dies, but both (girls and boys) do not have to be supported during the father’s lifetime.
Who is the author of our Mishna? It is difficult to say that it follows Rabbi Meir's opinion, as he says it is only a mitzva (not obligation) to support boys. It is difficult to say it follows Rabbi Yehuda's opinion, as he says that boys are also a mitzva. It is difficult to say it follows Rabbi Yochanan ben Beroka's opinion, as he says it is only a mitzva to support boys after the father dies.
The Gemora answers that the author could be any of these three Tanaim. Our Mishna could be Rabbi Meir, and it would read as follows: A father is not obligated to support his daughter and similarly his son, but there is a mitzva to support one’s daughter and certainly his son. Why did it only say “daughter” in the Mishna? This teaches us that it is even a mitzva to support a daughter (though she does not learn Torah), but it is not obligatory.
Alternatively, the Gemora answers that it could also be Rabbi Yehuda. The Mishna would read as follows: A father is not obligated to support a daughter and certainly a son, but it is a mitzva to support a son and certainly a daughter. Why does the Mishna only discuss a son? This teaches us that there is no obligation to support one's children, even regarding a daughter.
Alternatively, the Gemora answers that it could also be Rabbi Yochanan ben Beroka. The Mishna would read as follows: A father is not obligated to support a daughter or a son, and it is not even a mitzva to do so. The Mishna only used the term “obligation” (not to imply it is a mitzva, but rather) because there is an obligation to support daughters after their father dies.
Rabbi Ila said in the name of Reish Lakish in the name of Rabbi Yehuda bar Chanina: In Usha they decreed that a person must support his sons and daughters when they are minors.
The Gemora inquires: Does the halachah follow this decree or not? We can answer this from Rav Yehuda, who would tell people who came before him with this question, “The alligator has children, and throws them on the people of the city?!” [This implies that he would tell people they should do so, but not enforce it.] Rav Chisda would tell people who came before him: “Turn over a grinder in public stand on top of it and say: “a raven feeds its kin, and this person does not want to do so!”
The Gemora asks, does a raven indeed feed its kin? Doesn’t the passuk say “He feeds the sons of the raven who call out to Him?” This is not difficult, for the passuk is talking about the white ravens babies, while Rav Chisda meant the older black raven children (see Rashi).
When people would come before Rava, he would say: “Are you happy that your children should be supported from charity?” All of this is only referring to a case where the person is not wealthy. If he is wealthy, we force him to support his children. This is as in the case where Rava forced Rav Nasan bar Ami (regarding giving proper amounts of charity), and took from him four hundred zuz (type of coin) for charity.
Tosfos comments: If one has children less than six years old, he has an obligation to feed them, and it is enforceable. It would seem that this is a Rabbinical obligation.
Reb Moshe Feinstein in his sefer Dibros Moshe on Gittin (fourth perek; heora 83)writes the following novel halacha: If one has only one son and only one daughter, he is halachically required to support them. His reasoning is as follows: There is a mitzva of procreation. We hold according to Rabbi Yochanan, who states that if one has children and they die, he has not fulfilled his mitzva of procreation. Accordingly, if one does not sustain his children and they consequently die, he will be lacking his mitzva of peru u'revu. It is therefore incumbent upon him to be concerned about the welfare of these children; not necessarily for their sake, but for his mitzva.
He adds: When the Mishna says that one is not obligated to sustain his children, that is only if he has more than one son and one daughter. He concludes that he is bewildered why none of the poskim rule accordingly.