Gemara

(Rav Nachman): At first, I never collected from orphans' property;

After I heard Rav Huna cite Rav to say that orphans who consume others' (i.e. creditors') property should follow their father (i.e. die), I collect from their property.

Question: Initially, why didn't he collect?

Answer #1 (Rav Papa): Paying a creditor is a Mitzvah. Minors are exempt from Mitzvos.

Answer #2 (Rav Huna brei d'Rav Yehoshua): Perhaps the father gave Tzrari (a security) to his creditor.

These answers differ about one who admitted (just before he died) that he still owes, or if he was excommunicated for not paying and died in Niduy. (Had he paid, he would have done so in Beis Din so they would end the Niduy.)

The Halachah follows Rav Huna brei d'Rav Yehoshua.

Kesuvos 87a (Rabah citing R. Chiya): If a man wrote '(I have against you) no vow and no oath', he cannot make her swear (before paying her Kesuvah), but his heirs can;

If he wrote 'clean vow, clean oath', neither he nor his heirs can make her swear.

(Rav Nachman, citing Aba Sha'ul ben Eima Miryam): Whether he wrote 'no oath', 'clean oath'... 'from my property' or 'from these properties', neither he nor his heirs can make her swear;

However, what can I do? We learned that one can collect from orphans' property only if he swears!

91b: A man owed 100 Zuz. He died, and the only land he left was a plot worth 50 Zuz. The creditor took it for partial payment. The orphans gave him 50 Zuz (and took the land back). The creditor took it again for final payment.

(Abaye): It is a Mitzvah for orphans to pay the debt of their father. The 50 Zuz they gave the creditor was l'Shem Mitzvah. The creditor was entitled to take the land.

However, if the orphans said that the 50 Zuz is the value of the land, they expel him from it.

Bava Kama 94b (Beraisa): If a man died, and left to his orphans money that he collected for Ribis, even if they know this, they need not return it. If he left them a cow, garment or any specific item, they must return it due to the honor of their father.

Question: Why must they honor their father? "Do not curse a Nasi of your nation" refers to one who acts like your nation!

Answer: We answer like Rav Pinchas answered (elsewhere). The case is, the father repented (and died before he was able to return it).

112a: After R. Yirmeyah's father-in-law died, his son (a minor) locked the door of his father's house to prevent R. Yirmeyah from making a Chazakah on it.

R. Yirmeyah: I have witnesses that I made a Chazakah on the house in his father's lifetime!

R. Avin: We do not accept witnesses in the defendant's absence. A minor is not considered to be present!

Bava Basra 7b: Orphans had a loan document (of their father). A receipt said that it was paid.

Rav Chama: We do not let the orphans collect, lest it really was paid. We do not tear their document. Perhaps when they grow up, they will show that the receipt is invalid.

Rishonim

Rambam (Hilchos Malveh 11:6): A Milveh Al Peh is collected from orphans in only one of three ways. 1) Reuven (the borrower) admitted and commanded while sick that he still owes Ploni. 2) The loan was for a set time, and it did not arrive yet (when Reuven died), and there is a Chazakah says that a man does not pay before the time. 3) Reuven was excommunicated until he will pay and he died in Niduy. In these three cases, we collect from orphans without a Shevu'ah. If Ploni showed a document written in Kesav Yado (Reuven's handwriting), he does not collect with it at all.

Rosh (Kesuvos 11:24): If the borrower died before the loan was due, there is a Chazakah that a man does not pay before the time, and the lender collects from the heirs.

Rosh (Bava Basra 1:9, citing R. Yonah): Even though we are not concerned for payment within the time, we are concerned for Tzrari even within the time. People are wont to deposit Tzrari within the time, and even at the time of the loan. This is why the Gemara explained that we do not collect from orphans due to Tzrari. It did not say that the concern is for payment, to teach that we are concerned even within the time.

Hagahos Ashri, citing Mahari'ach: If the father was alive, he would not be believed to say 'I paid'. Therefore, we do not claim this for the orphans. This is only from adult orphans. We do not collect from minor orphans. This is not only when we must accept witnesses, which cannot be done in front of minors (it is as if they are not here). Rather, even if witnesses testified in their father's lifetime, and Beis Din gave him time to pay and he died within the time, we do not collect from minors until they mature, unless there is Ribis (on a Nochri's loan) or to pay a Kesuvah and exempt the orphans from feeding her. Regarding minors, we are concerned for Tzrari even within the time.

Tosfos (Kesuvos 86a DH Pri'as): It is a Mitzvah (for children to pay their father's debt) if they inherited land. Even so, we do not collect from minors, since they are not commanded about Mitzvos. If there is no Acharayus Nechasim (they did not inherit land), it is a Mitzvah for the heirs to pay, but we do not force them. This is clear from 91b. The reason we do not force them is because the reward for honoring (parents) is explicit in the Torah, therefore Beis Din is not commanded (to enforce it). In Bava Kama, we obligate them to do so. There (he stole, so) if they would not return it, it would be disgraceful. For mere honor, we do not force them. Rashi said regarding the plot of Abaye that since the Mitzvah is only mid'Rabanan, we do not force them. This is wrong. We force regarding mid'Rabanan laws, e.g. to fulfill the command f the Niftar!

Tosfos (Bava Basra 5b DH v'Afilu): The Gemara says that one must swear to collect from orphans, i.e. adult orphans. One may not collect from minors, even within the time according to Rav Papa. Even Rav Huna holds that one cannot collect within the time because we cannot accept testimony against them. Even in front of is like in their absence (Bava Kama 112a). Even if testimony was accepted in their father's lifetime, we can say that we are concerned for Tzrari, even within the time.

Poskim

Shulchan Aruch (CM 108:1): A Milveh Al Peh is collected from orphans in only one of three ways. 1) Reuven (the borrower) admitted and commanded while sick that he owes Ploni. 2) The loan was for a set time, and it did not arrive yet (when Reuven died). 3) Reuven was excommunicated until he will pay, and he died in Niduy. In these three cases, we collect from orphans without a Shevu'ah. However, if witnesses testified that Reuven owed Ploni, he does not collect from the heirs at all, lest he paid.

Shulchan Aruch (3): We do not collect from minors below 13 years any loan of their father, even if the lender has a validated document, and even if there was any stipulation in the world that the lender will be believed, lest they have a proof that breaks the document.

Gra (11): This is because the Gemara did not list these among differences between Rav Papa and Rav Huna.

SMA (12): It does not matter whether the heirs are children, brothers or other heirs, and even if they have an Apotropos.

Shulchan Aruch (ibid.): The only exceptions are the three mentioned above (in Sa'if 1), for which we collect even a Milveh Al Peh. Regarding a loan within the time, we must say that the testimony was in the father's lifetime, for if not, we do not accept testimony against a minor, even in front of him.

SMA (13): When the father admitted before he died, those who received the command knew that he owed. For such clear matters, we accept testimony even in front of minors. However, the Tur and Shulchan Aruch (110:9) require that he command in front of Beis Din, or write it in his handwriting and Beis Din recognizes it. Also if he dies amidst Niduy, the matter is known. Sa'if 1 discusses adult orphans, so we accept testimony in front of them, therefore it equated all three ways.

Pischei Teshuvah (2): Sha'ar Mishpat (4) says that when the law is not known (e.g. one is entitled to collect his expenses, but we do not know how much they were - CM 158:8), the Rambam and Shulchan Aruch holds that the claimant swears while holding an item, and collects. If so, he cannot collect from orphans. The Ramah, Ramban and Shach hold that in such a case there is even a stronger Chazakah that he did not pay than a loan within the time, if so he collects from minor orphans just like a loan within the time.

Shulchan Aruch (ibid.): If one brought a validated document against adult orphans, even if it is not one of the ways above he collects without a Shevu'ah if there is explicit Ne'emanos in the document. I.e. the borrower trusted the lender against him and his heirs or Ba'ei Kocho (those one who received their rights from him), for his heirs are included in Ba'ei Kocho.

Beis Yosef (DH u'Mah she'Chasav v'Im): Tosfos (Kesuvos 86a) showed that adult orphans must pay even according to Rav Papa. We are forced to say that we collect from orphans only in three cases, i.e. minor orphans.

Beis Yosef (DH Kasav Rabbeinu): R. Yerucham (26:3 76a) says that if a loan document was brought against orphans, and they say that they did not inherit anything, they need not swear to this. The Tur (69) wrote that we make a Stam Cherem. However, R. Yerucham connotes that if the lender claims Vadai that they inherited land, and they deny it, they must swear.

Gra (14): If the document is not validated, we claim that perhaps it is forged,

Shulchan Aruch (ibid.): If there is no Ne'emanos, or there is Stam Ne'emanos but he did not specify 'against my heirs' or 'against Ba'ei Kochi', to collect he must swear an oath like a Torah oath, while holding a (Kodesh) object. Even if he seized property from them without a Shevu'ah, we make him swear.

Beis Yosef (DH u'Mah she'Chasav Ela): One must swear in order to collect from orphans because we claim for orphans whatever their father could have claimed. Their father could have demanded 'swear to me that it was not paid.' Therefore, even though the heirs did not say this, we say it for them.