1) THE EXEMPTION OF A MINOR FROM PUNISHMENT FOR ADULTERY
QUESTION: The Gemara expounds from the word "Ish" (Vayikra 20:10) that "'Ish' Prat l'Katan" -- a Katan who commits adultery is exempt from punishment. Why does the Gemara need to learn this exemption from a verse? A Katan is never liable for punishment.
ANSWERS:
(a) TOSFOS explains that one might have thought that a Katan who commits adultery with an adult woman should be killed since the woman is killed because of him. Tosfos in Erchin (3a) compares the case of a Katan who commits adultery with an adult woman to the case of a person who has relations with an animal. The Gemara in Sanhedrin (55a) teaches that when a person has relations with an animal, the animal is put to death because it brought about the death of a person and its presence causes constant shame to the deceased. One might have thought that a Katan who commits adultery with an adult woman should be killed for causing the death of the woman.
(b) The RA'AVAD (cited by the Rishonim) explains that with regard to transgressions of immorality (Arayos), even an act of "Mis'asek" requires atonement. When one commits a sin of Arayos inadvertently he is obligated to bring a Korban because he derived physical benefit from the Aveirah. Accordingly, one might have thought that a Katan also should be obligated to bring a Korban even though his act was comparable to "Mis'asek" in that it was done without Da'as (intellectual awareness).
(c) The RAV AVAD (cited by the Rishonim), the father-in-law of the RA'AVAD, answers that the verse indeed does not exempt the Katan from punishment; he is already exempt by virtue of his age. Rather, the verse exempts the adult woman who sinned with the Katan (when the Katan is under nine years old). (The Katan in this case is not the same as the Katan mentioned in the end of the Beraisa which discusses "Eshes Katan," because the Beraisa there refers to a child who is over nine years old.)
2) YI'UD WITH CONSENT
QUESTION: Rebbi Yanai teaches that Yi'ud may be performed only with the knowledge of the Amah Ivriyah. He derives this from the verse, "Asher Lo Ye'adah" (Shemos 21:8), in which the word "Ye'adah" is understood to imply "De'ah" (knowledge or consent).
How is Rebbi Yanai's teaching to be reconciled with the Gemara earlier (5a) that states that the money paid to acquire an Amah Ivriyah accomplishes the Kinyan even against her will?
ANSWERS:
(a) RASHI earlier (5a, DH b'Amah) writes that only the sale of the Amah Ivriyah may be done against her will, but not the Kidushin (Yi'ud). Although the sale requires the father's consent, since the sale does not require the daughter's consent the Gemara there mentions it as an example of a Kinyan against a person's will.
(b) TOSFOS (5a, DH she'Ken) disagrees with Rashi and explains that since the sale is done with the consent of the father, it is not considered a Kinyan against a person's will. Rather, the Gemara there means that when Kesef creates the Yi'ud of an Amah Ivriyah, it does so against the will of both the father and the Amah (according to the opinion that the money given for the purchase of the Amah is not what effects the Kidushin -- "Ma'os ha'Rishonos Lav l'Kidushin Nitnu").
Accordingly, Tosfos there explains that the Gemara here does not mean that Yi'ud must be done with the consent of the Amah, but it means that Yi'ud must be done with her knowledge. She must be informed that Yi'ud is being done, but her consent is not necessary.
However, other statements in the Gemara here (19a-19b) seem to contradict the approach of Tosfos. Rava derives from the laws of Yi'ud that a man may instruct his daughter (who is a Ketanah) to accept her own Kidushin in his place. This implies that when she performs Yi'ud, the Amah willingly accepts the Kidushin that the master gives her (according to the view that "Ma'os ha'Rishonos Lav l'Kidushin Nitnu") and it is not done against her will.
Similarly, the Gemara (19b) compares the case of Yi'ud (according to the opinion that "Ma'os ha'Rishonos Lav l'Kidushin Nitnu") to the case of a man who says to a woman, "You are hereby betrothed to me after thirty days pass," and he does not say "me'Achshav" -- "from now." In order for such a Kidushin to take effect, the woman must consent at the time the Kidushin is slated to take effect. (See RASHI to 19b, DH l'Rebbi Yosi.) This implies that Yi'ud takes effect only with the Amah's consent.
Tosfos, however, understands those statements of the Gemara differently from the way Rashi explains them. Tosfos here (DH Omer) explains that when Rava rules that a man may instruct his Ketanah daughter to accept Kidushin, he means merely that she is able to receive (and acquire) the money of the Kidushin herself; he does not mean that she may choose which man to marry. Tosfos explains the second Gemara later (19b) differently as well (see TOSFOS DH Mashal).

OTHER D.A.F. RESOURCES
ON THIS DAF