Gemara

42a (Mishnah): If Reuven deposited coins with Shimon, and Shimon gave them to his small children (minors) to guard (and they were lost), he is liable, for this is not the way people guard.

A case occurred in which Reuven deposited coins with Shimon, who gave them to his mother to guard. She put them in a chest, and they were stolen.

(Rava): We cannot obligate Shimon or his mother. A depositor expects the Shomer to entrust the deposit with (adult) members of the Shomer's family, and she was not told that it was another's money and she should bury it!

98b (Mishnah): If Reuven lent to Shimon a cow, he sent it with his own or Shimon's son, slave or Shali'ach, and it died, Shimon is exempt.

The same applies to returning it.

Bava Basra 87b (Mishnah): If Reuven sent his son (with a flask) to a grocer (Shimon), who gave to him oil, and the child broke the flask, Shimon is liable;

R. Yehudah exempts him, for he did like Reuven wanted.

Chachamim agree that if the child held the flask and Shimon measured into it, he is exempt.

Question: Why do Chachamim obligate him? Reuven knowingly gave it to his son (who is prone to break it)!

Answer (Rava and R. Zeira): The case is, Shimon took it to measure for others. R. Yehudah holds that one who borrows without permission is like a borrower. It suffices to return it to where he took it from (the child). Chachamim hold that such a borrower is like a thief, and he must return it to the owner.

Rishonim

Rif and Rosh (Bava Metzia 3:23): Rava taught that a depositor expects the Shomer to entrust the deposit with members of the Shomer's family.

Rosh: If people of the Shomer's family were negligent, the Shomer is liable. If the Shomer would be exempt, his wife and children would consume the deposit, for also they are exempt (they have no money to pay)!

Rif and Rosh (Bava Basra 44b and 5:20): Chachamim hold that one who borrows without permission is a thief, therefore, it is in his Reshus. Even if he returned it to the child, he is not exempt until he returns it to the owner.

Rambam (Hilchos Gezeilah 3:15): If Levi's child or slave was holding a flask, and Ploni took it and used it, he is liable for Ones until he returns it to Levi. Therefore, if he returned it to the minor who was holding it or the slave and it was lost or broken, Ploni must pay. The same applies to all similar cases.

Magid Mishneh: A slave is like a child. As long as Ploni did not return it to the owner, he is liable.

Lechem Mishneh: A slave is unlike a child! A slave has Da'as (understanding). He is his master's Shali'ach. This is like one who returned a flask to its place. He is exempt, for it is guarded there!

Rambam (Hilchos She'elah 4:8): One who deposits money or Kelim with Ploni intends that they will be entrusted to Ploni's wife, adult children and household. If Ploni gave it to his minor children, or minor or adult slaves, or a relative who does not live in the house with him, he is liable, unless the second Shomer proves that he was not negligent.

Magid Mishneh: One does not entrust his property with his slave.

Mordechai (Bava Metzia 272, citing Maharam): If Shimon returned Reuven's deposit to Reuven's wife, and she has Da'as and Reuven lets her buy and sell, Shimon swears and he is exempt, for Reuven trusts her with everything. Also, a depositor expects the Shomer to entrust it with members of the Shomer's family; this is similar.

Maharik (77): Since Reuven lets his wife buy and sell, it is as if he normally deposits everything with her.

Poskim

Shulchan Aruch (291:21): One who deposits money or Kelim with Ploni intends that they will be entrusted to Ploni's wife, (Rema - adult) children and household.

SMA (31): This is because the depositor knows that Ploni cannot be in his house constantly to guard the deposit.

Maharshach (2:85): This refers only to a Shomer Chinam. A Shomer Sachar is paid to guard well, day and night (She'altos). He is liable for theft even though it is close to Ones. If a servant stole the deposit, this shows that the servant was not established to be Kosher; he is like a slave. Even if Ploni was a Shomer Chinam, he is liable for allowing such a person to access the deposit.

Shach (27): Teshuvas Ri l'Beis Levi (87) challenged this, for the Beis Yosef brought that argue with the Rambam, and exempt a Shomer who gave to an inferior Shomer if the owner regularly used the latter. (This shows that the exemption is not limited to a Shomer Chinam.)

Rema: Similar, if the Shomer returned to the owner's wife, he is exempt. See Siman 340:8.

Shulchan Aruch (ibid): If Ploni gave it to his minor children, or minor or adult slaves, or a relative who does not live in the house with him and eat from him, and all the more so if he gave it to someone else, Ploni is liable, unless the second Shomer proves that he was not negligent.

Beis Yosef (DH u'Mah she'Omar): Stam slaves are thieves.

Darchei Moshe (10): This refers to Kena'ani slaves. One who gave to an Eved Ivri is exempt, like one who gave to his son or daughter.

Rema: The same applies if Ploni allowed others to enter where the deposit was kept. Even if those who entered were not established thieves, Ploni is liable if it was stolen, for this is negligence.

Rema (340:8): Some say that if a borrower returned the item to the lender's wife and Ones occurred, he is liable.

Beis Yosef (DH Kosav ha'Rashba): The Rashba (2:262) says that if a borrower returned the Keli to the owner's wife or children who eat from his table, and it was stole, he is liable. We learn from the Mishnah (98b). The owner must know when it is returned. This is like R. Eliezer (31a), who requires informing the owner in every case except for Hashavas Aveidah.

Darchei Moshe (1): One who deposits with Ploni intends that they will be entrusted to Ploni's household. Perhaps a borrower is different.

Taz and SMA (12): A borrower is different, for he gets all benefit (so he has more liability, and must return it to the lender himself).

Rema (120:2): If a borrower paid the lenders wife, he was Yotzei.

Gra (7): The Rema (291:21) wrote similarly about returning a deposit. This is from the Maharam in the Mordechai, and Teshuvas Maimoni (Mishpatim 3). In Siman 340:8, the Rema rules like the Rashba, who argues. The Acharonim strained to resolve them, but in truth they argue. The Rashba's opinion is primary. Regarding returning, we do not say that one deposits with intent for his family (Bava Metzia 98b). The same applies to a loan, for Bava Kama 104a equates returning theft and returning a loan.

Shulchan Aruch (366:3): Sho'el she'Lo mi'Da'as is a thief. If Levi's child or slave was holding a flask, and Ploni took it and used it, he is a Sho'el she'Lo mi'Da'as, and it is in his Reshus to be liable for Ones until he returns it to Levi. Therefore, if he returned it to the minor who was holding it or the slave and it was lost or broken, Ploni must pay.

SMA (8): The Rambam said that if Ploni returned it to Levi's slave, he is liable. The Tur and Shulchan Aruch (291:21) agree.