פירוש על בבא בתרא 5:9

השולח בנו – minor [child] with the storekeeper and in his hand was a Duponium/a Roman coin equal to two Asses which are two Issarim to bring to him an Issar of oil. And he will give him another Issar. And this is what he did. But the young child broke the flask and the oil spilled and he lost the Issar that the storekeeper gave him. The storekeeper is liable for oil, and for the flask and for the Issar, for the father did not send his minor-age child to the storekeeper other than to inform him that he needs oil, not that he should send the oil through his (i.e., the child’s) hand. And in the Gemara (Tractate Bava Batra 87b-88a), it raises the question: why is the storekeeper liable for the flask? It is a loss with consent. For he himself (i.e., the father) sent it in the hand of his son, and [the Gemara] answers for example that the storekeeper took it to measure oil for others. Therefore, he became a thief concerning it. And it exists in his domain until he returns it to the mater. And even though he returned it to the young child, he is not exempt from it.

Introduction Mishnah nine deals with a father who sends his small child to buy oil from a shopkeeper and on the way home the son drops the flask of oil.

רבי יהודה פוטר שעל מנת כן שלחו – for just as the storekeeper sent it in the hand of his son

If a man sent his child to a shopkeeper with a pondion (a in his hand and he measured him out an issar’s (a coin worth half a worth of oil and gave him an issar in change and the child broke the flask and lost the issar, the shopkeeper is liable. Rabbi Judah declares him exempt, since the father sent the child for this purpose. And the Sages agree with Rabbi Judah that if the flask was in the child’s hand, and the shopkeeper measured the oil into it, the shopkeeper is exempt. In the scenario in our mishnah a father sends his child to a store to buy him some oil. The shopkeeper hands him a flask containing the requested oil and the change from the sale. According to the Sages, if the child should lose the oil or the coin on his return home, the shopkeeper is liable to pay back the father. Since a child is not responsible for his actions, the shopkeeper should have found a safer way of returning the oil and coin to the father. Rabbi Judah disagrees. According to him, since the father sent the child on such a mission, the father agreed to allow his child to deliver the oil and the change. The Sages agree with Rabbi Judah that the shopkeeper is not liable only in the case where the child came to the store with a flask in his hand. In such a case it is clear that the father intended that the child should deliver the oil, and therefore the shopkeeper will be exempt.

שהוא פטןר – from the cost of the flask, but the Halakha is not according to Rabbi Yehuda.