Gemara

(Beraisa - R. Meir): A Katan or Ketanah (minor boy or girl) may not do Yibum or Chalitzah.

Chachamim: We agree that a Katan may not do Chalitzah. It says "Ish," and the Torah equates the Yevamah to the Yavam.

Yevamos 104b (Mishnah): Chalitzas Katan is Pasul;

If she was a minor, she does Chalitzah again after she matures. If not, the Chalitzah was Pasul.

105b (Rav Yehudah): This is like R. Meir, but Chachamim say that a Ketanah may do Chalitzah.

The Chachamim hold like R. Yosi;

A Yevamah came in front of Rebbi (to do Chalitzah). He told Avdan to check whether or not she is an adult.

R. Yishmael bar R. Yosi, citing R. Yosi: "Ish" teaches that the Yavam must be an adult, but she may be an adult or minor.

Rebbi: There is no need to check her. The elder has already ruled.

(R. Ami): From R. Yosi, we learn that a Yevamah may do Chalitzah from the age of Pa'utos (six to 10, depending on how sharp she is).

(Rava): She must reach the age of vows (one year before adulthood).

The Halachah is, she must bring two hairs (of adulthood).

Rishonim

Rif (Yevamos 34a): If she was a minor, she does Chalitzah again when she becomes an adult. If not, the Chalitzah was Kosher. (Note: in some versions of the Rif it says 'Pasul'.)

Rif and Rosh (12:13): Rav Yehudah taught that our Mishnah is like R. Meir, but Chachamim say that a Ketanah may do Chalitzah. The Halachah is, she does not do Chalitzah until bringing two hairs.

Rambam (Hilchos Yibum u'Chalitzah 4:16): Chalitzas Ketanah is Pasul. Chalitzas Katan is not Chalitzah.

Magid Mishneh: Some are unsure about Chalitzas Ketanah b'Di'eved. Since the Gemara requires waiting for two hairs, this connotes that b'Di'eved it is Pasul, like the Rambam says. Some texts say that b'Di'eved it is Kosher. This is a printing mistake.

Rosh (ibid.): If she was a minor, she does Chalitzah again when she becomes an adult. If not, the Chalitzah was Pasul. The Yerushalmi's text says 'if not, it was Kosher', and this is the Rif's text.

Tosfos (105b DH Ketanah): Since it was taught that the Chalitzah is Pasul, why does it teach that she does Chalitzah again after she matures? Also, this was not taught regarding Chalitzas Katan! I answer that had it not been taught regarding a Ketanah, one might have thought that the Chalitzah is Pasul mid'Rabanan. The Hekesh equating the Yevamah to the Yavam is not mid'Oraisa. Therefore, it says that she does Chalitzah again after she matures, to teach that Chalitzas Ketanah is totally void, like Chalitzas Katan. However, the Yerushalmi's text says 'if not, it was Kosher.' I.e. R. Meir equates a Ketanah to a Katan only mid'Rabanan. R. Yosi permits Chalitzas Ketanah l'Chatchilah, like the episode with Rebbi. Also the Yerushalmi establishes the Mishnah like R. Meir.

Terumas ha'Deshen (225): If a Ketanah did Chalitzah, when she repeats Chalitzah after maturity, she need not do Chizur (Chalitzah with all the brothers). Even according to the Ge'onim who rule like Rav, that Chalitzah Pesulah requires Chizur, here it is not needed. Tosfos concluded that Chalitzas Ketanah is totally void mid'Oraisa. However, the Yerushalmi connotes that R. Meir equates Ketanah to Katan only mid'Rabanan. Our text holds that it is totally void, so she does not need Chizur. The Yerushalmi's text is Machshir the Chalitzah. We are stringent to require another Chalitzah, but we are not so stringent to require Chizur. No one requires Chizur in such a case. This does not require a proof. The Rambam holds that the Chalitzah was Pasul. He would require Chizur. However, he was not meticulous to explain the extra words in the Mishnah. However, some great Chachamim rule unlike Rav and never require Chizur. Tosfos does not require Chizur even according to Rav, and the Rif holds that Chalitzas Ketanah is Kosher b'Di'eved. We rely on all these opinions, for only the Rambam require Chizur. Chizur is a stringency mid'Rabanan. In such matters we follow the lenient opinion.

Poskim

Shulchan Aruch (EH 169:49): If a minor Yevamah did Chalitzah with an adult, it is Pasul, and it disqualifies her to all the brothers.

Beis Yosef (DH u'Mah and DH Ketanah): The Tur says that the Rosh equates Chalitzas Ketanah to Chalitzas Katan. I did not find so in the Rosh. Tosfos says so. Why did the Tur say so in the name of the Rosh? Also, Tosfos did not say that this is the truth, for afterwards Tosfos brought the Yerushalmi, which says that if she does not repeat Chalitzah after maturity, it is Kosher. Tosfos was unsure about the text. How can one say in the name of Tosfos that it is totally void, just like Chalitzas Katan?! The Rif's text is like the Yerushalmi. In any case, since we rule that she must bring two hairs, this connotes that Chalitzah before this is Pasul. The Rambam says so.

Drishah (85) and Bach (29): The Beis Yosef erred. 'It is nothing' does not mean that she may do Yibum. Tosfos explained R. Meir, and the Gemara explicitly says that R. Meir equates Chalitzas Ketanah and Chalitzas Katan. Both forbid Yibum. Tosfos merely explains the extra words of R. Meir. It was obvious that mid'Oraisa, Chalitzas Katan is totally void, for it says "Ish". One might have thought that a Ketanah can do Chalitzah, for the Torah does not equate her to him. Mid'Rabanan we equate them. Therefore, R. Meir taught that also Chalitzas Ketanah is totally void mid'Oraisa.

Drishah: The Rosh concluded 'the Halachah is, she does not do Chalitzah until bringing two hairs.' The Tur derived that we do not hold like Chachamim, who distinguish between a Katan and Ketanah.

Bach: Afterwards, Tosfos brought the Yerushalmi's text. He explains that even though Chalitzas Ketanah is Kosher b'Di'eved, l'Chatchilah she must do Chalitzah after bringing two hairs. This is all according to R. Meir. Chachamim hold like R. Yosi, that the Torah is Machshir Chalitzas Ketanah, and the Amora'im were stringent to wait for two hairs. Perhaps they disqualify Chalitzas Ketanah mid'Rabanan. Or, perhaps they rule like R. Meir. I say that the Tur derived the Rosh's opinion from the fact that he brought Rav Yehudah's teaching that the Mishnah is R. Meir, but Chachamim disagree. Since we require until two hairs, the Halachah follows R. Meir, and not Chachamim! Sefer ha'Terumah and Semag say so (that since we require two hairs, the Halachah follows R. Meir). Why did the Rosh bring Rav Yehudah? One might have thought that Chalitzas Ketanah is Pasul, like R. Meir. Rav Yehudah teaches that mid'Oraisa, no Chalitzah is Pasul. Chalitzas Katan is totally void, and Chalitzas Ketanah is Kosher. The Amora'im merely teach that l'Chatchilah she must wait for two hairs, but b'Di'eved it is Kosher.

Bach: The Rosh merely cited the Rif, so one could infer similarly from the Rif. The Tur cited the Rosh to teach that even though the Rambam saw the Rif and explained differently, the Rosh agreed with the Rif. I explained the Tur, but the Rambam's opinion is primary. Chalitzas Ketanah forbids Yibum, for Chachamim hold that it is Kosher.

Bach (28): The Magid Mishneh says that since we rule that she must bring two hairs, this connotes that Chalitzah before this is Pasul, like the Rambam says. The Nimukei Yosef said that perhaps it is Pasul even b'Di'eved, like R. Eliezer in the Tosefta. The Ritva says that the law is not clear, so we are stringent. Perhaps the Rambam is stringent because it is not clear whether the Chalitzah disqualifies to the brothers, or does nothing. Therefore, we are stringent. The primary explanation is that the Rambam rules like Chachamim, that even a Ketanah can do Chalitzah, but the Amora'im were stringent l'Chatchilah to wait until two hairs. Surely, even without two hairs she is disqualified to the brothers.

Beis Shmuel (49): Our text says that if she does not repeat Chalitzah after maturing, it is Pasul. Tosfos derives that it is totally void, just like Chalitzas Katan. I.e. it does not forbid Yibum. Even though the Gemara says that Chachamim do not equate the Yevamah to the Yavam, we rule unlike Chachamim, for we conclude like Rava, that she must bring two hairs. Also Semag says so. The Rosh holds that this text is primary. Therefore he concludes that Chalitzas Ketanah is totally void. This is why the Tur says that the Rosh holds that it is like Chalitzas Katan. This was the Beis Yosef's understanding of Tosfos. Even though Tosfos said so according to R. Meir, who holds that even Chalitzas Katan disqualifies, from R. Meir we learn to Chachamim. We hold like Chachamim, that Chalitzas Katan does not disqualify. If so, also Chalitzas Ketanah does not disqualify. The extra words in the Mishnah teach that the Hekesh is mid'Oraisa. This answers the questions of the Bach and Drishah against the Beis Yosef. The Rif's text says that if she did not do Chalitzah again after maturing, it is Kosher. The Amora'im say to wait for two hairs l'Chatchilah.

Beis Shmuel: The Rambam said that it is Pasul, like our text, unlike the Magid Mishneh. (Hagahos Ma'aseh Nisim - he refers to the Magid Mishneh on 5:23, who says that the Rambam's text says that b'Di'eved it is Kosher.) Tosfos asked why the Gemara needed to say that she repeats Chalitzah after maturity. The Rambam can answer differently. Even though we equate this to Chalitzas Katan only mid'Rabanan, she needs another Chalitzah after maturity. There are three opinions about Chalitzas Ketanah. Tosfos holds that Chachamim hold that it is not Chalitzah at all and it does not disqualify. The Rif is Machshir b'Di'eved. The Rambam disqualifies and requires another Chalitzah. The Magid Mishneh says that according to the Rif's text, we conclude that even b'Di'eved Chalitzas Ketanah is Pasul. This is difficult, for in the Rif's text, even R. Meir is Machshir! How can Rava rule unlike all the Tana'im?!

Gra (135): Also the text in Gitin 24b says that it is Pasul.

Rema: When she matures, she does Chalitzah with one of them. She need not do Chalitzah with all of them.