Tosfos shows that you can have a Ger Katan d'Oraisa by showing that if a mother goes to the Mikveh the kid doesn't have to go the Mikveh later in life. But my question is that even though this kid doesn't have to go through any "updated Gerus" when he's older because he is seemingly born a full fledged Jew, he is none the less called a Ger...So can he eventually be Mocheh when he is older? Was it his Da'as that accepted this "Gerus"? There are even Hava Amina's that say this baby could be a Chatzitzah proving he's his own entity...
Ben Greene, Oak Park
There is a lot of discussion among the Poskim as to whether this baby may be Mocheh when he is older.
1) The Avnei Milu'im (written by the author of the Ketzos ha'Choshen) in Even ha'Ezer 4:4 (DH Me'uberes) writes that he may protest against the original Gerus when he grows up.
a) His proof is from the Gemara in Yevamos 78a. The Gemara cites a general question concerning the Halachic status of a fetus. One opinion maintains that "Ubar Yerech Imo" -- the fetus is considered the "thigh" of the mother. In other words, the unborn child is considered an integral part of the mother, like her thigh. The other opinion maintains "Ubar Lav Yerech Imo" -- the fetus is not like the thigh or any other limb of the mother, but rather it has an independent identity.
b) The Gemara then challenges the opinion that the fetus is considered an independent entity from the ruling of Rava who says that if the pregnant mother goes to the Mikvah, the child does not have to go to the Mikvah later in life. If the baby is an independent entity, then the mother's immersion does not automatically work to make him a Ger as well! In the end, the Gemara answers that the Tevilah of the fetus is effective because the mother is not a Chatzitzah between the fetus and the water, since it is the natural state that the mother always covers the baby she is carrying.
c) The Avnei Milu'im writes that we see from the Gemara that the reason why the immersion is effective for the fetus is not that he is part of the mother's immersion, but rather because the baby himself underwent his own effective Tevilah. The Avnei Milu'im concludes that, if so, the fetus that did Tevilah is the same as the child who did Tevilah in Kesuvos 11a. In the same way that the child may be Mocheh later on, the fetus may be Mocheh later on.
d) The Avnei Milu'im summarizes this in Siman 13:5 (DH v'Ika). If he was conceived before the mother converted, the fetus is considered the same as a minor Ger who is immersed with the help of the Da'as of the Beis Din. Therefore, he can be Mocheh later on. If he was conceived after the mother's conversion, he is considered as having been born totally Jewish and cannot be Mocheh later on.
2) The Chasam Sofer writes in a Teshuvah (Yoreh Deah #253) that the baby cannot be Mocheh later on.
a) The Chasam Sofer writes that even if the parents brought the child to Beis Din after he was born in order to do Gerus, he also cannot be Mocheh later. Accordingly, if he was in his mother's womb at the time of her Tevilah, this is an extreme case of the mother bringing the child in front of Beis Din to receive Gerus, and he certainly cannot protest later on. The only time that the child can later be Mocheh is when he came on his own to ask for Gerus.
b) The Chasam Sofer provides support for this Chidush from the fact that it resolves seemingly contradictory passages in the Rambam. The Rambam, in Hilchos Isurei Bi'ah 13:7 (which is the chapter in the Rambam devoted to the Halachos of Gerus), does not mention the Din that when the Ger converted as a minor, he can be Mocheh later on. However, in Hilchos Melachim 10:3 (where the Rambam deals with the laws of Bnei Noach), he does mention that the child who underwent Gerus can be Mocheh. Why does the Rambam mention this Halachah only there, and not in Hilchos Isurei Bi'ah?
The Chasam Sofer writes that it is not a far-off suggestion to claim that there may be a difference between whether the minor came on his own or whether he was brought by his parents. If he was brougt by his parents he cannot protest later. If he came on his own he can protest.
Where is there an indication in the words of the Rambam in Hichos Isurei Bi'ah that the Rambam refers to a scenario where the Katan was brought by his parents, while in Hilchos Melachim he came on his own? The answer is that in Hilchos Isurei Bi'ah the Rambam goes through the laws of Gerus. He discusses the standard ways that Gerus comes about. Therefore, when he discusses the conversion of the minor, it is not necessary for the Rambam to write explicitly that his parents brought him, because it is unusual for a Katan to come to Beis Din on his own, without adult help, to ask for conversion. In addition, immediately after the Din of the minor coming to Beis Din, the Rambam cites the Din of the pregnant mother who did Tevilah for Gerus. Since the two Dinim are mentioned together, this implies that the minor coming to Beis Din is also coming with his parents.
In contrast, in Hichos Melachim, the Rambam describes how a Ben Noach converts to Judaism. First, the Rambam tells us the Din of the adult who cannot retract once he has done Gerus. Then, he tells us that the minor can retract later. Just as the first Din, about the adult, obviously means he came on his own, so the next Halachah, about the minor, also refers to a scenario where he came on his own.
3) I found that the Rogatchover Gaon zt'l wrote that the baby who did Tevilah for Gerus in his mother's womb is considered born as a full-fledged Yisrael, and not one born as a Ger.
a) His proof is from the first Mishnah in the eighth chapter of Bechoros (46a). The Mishnah states that if a woman underwent Gerus when she was pregnant, the baby later born is considered a Bechor, firstborn, for whom Pidyon ha'Ben must be done by giving five silver Shekalim to a Kohen. The Rogatchover writes (in Tzofnas Pane'ach on the Rambam, vol. 2, Terumos, p. 159, DH v'N'M) that if the baby would be considered a Ger it would not be possible to call him a Bechor, a Jewish firstborn. (Only a baby born Jewish can be considered a firstborn who must be redeemed from the Kohen.)
If he is considered born Jewish, it makes sense that he cannot be Mocheh later on to renounce his Jewishness.
b) The Rogatchover cites another proof that the Tevilah of the mother is effective to make the fetus Jewish. From the words of the Rambam (Hilchos Chovel u'Mazik 4:3), we see that the mother has a monetary claim on the fetus. The Rambam there discusses the case discussed of somebody who assaulted a pregnant woman and caused a miscarriage. Generally, the assaulter must pay damages to the father of the dead fetus, or if the father is no longer alive, he pays to the father's heirs. However, there is a scenario where there is no father and no heirs either. This is the scenario where the husband himself was a Ger and is no longer alive at the time of the assault and has no heirs either. In such a case, the Rambam writes that the mother receives the damages. This proves that the mother possesses a certain ownership of the baby in her womb.
If we now come back to the pregnant mother doing Tevilah, we can say that the Tevilah is effective for everything inside her body that she owns. This means that the Tevilah is effective for the fetus, and therefore, in the same way that the mother is Jewish by the time the baby is born, the baby is Jewish at the time he is born, and therefore he cannot be Mocheh on the Gerus later on.
Kol Tuv,
Dovid Bloom