סימן צד סעיף ז
צָרִיךְ לְזַכּוֹת דַּוְקָא עַל יְדֵי אַחֵר. וְלָכֵן לֹא יְזַכֶּה עַל יְדֵי בְּנוֹ וּבִתּוֹ הַקְּטַנִּים אַף עַל פִּי שֶׁאֵינָם סְמוּכִים עַל שֻׁלְחָנוֹ, מִשּׁוּם דְּיָדָם כְּיָדוֹ. אֲבָל עַל יְדֵי קָטֹן אַחֵר, יָכוֹל לְזַכּוֹת (דְּבְמִידִּי דְּרַבָּנָן, קָטֹן זוֹכֶה לַאֲחֵרִים). וְאִם אֶפְשָׁר, לֹא יְזַכֶּה עַל יְדֵי אִשְׁתּוֹ, שֶׁמַּעֲלֶה לָהּ מְזוֹנוֹת, וְגַם לֹא עַל יְדֵי בְּנוֹ וּבִתּוֹ הַגְּדוֹלִים אִם הֵם סְמוּכִים עַל שֻׁלְחָנוֹ, מִשּׁוּם דְּיֵשׁ אוֹמְרִים, דְּגַם אֵלּוּ נֶחְשָׁבִים כְּיָדוֹ. וּמִכָּל מָקוֹם בְּדְלֵית לֵיה אִישׁ אַחֵר יָכוֹל לְזַכּוֹת עַל יְדֵיהֶן. וְאִם הַבֵּן נָשָׂא אִשָּׁה, אַף עַל פִּי שֶׁסָּמוּךְ עַל שֻׁלְחַן אָבִיו, לְכֻלֵּי עָלְמָא יָכוֹל לְזַכּוֹת עַל יָדוֹ (שס"ו).
It is essential [that the maker of the eiruv] should grant them ownership only through a third party, therefore, he may not grant ownership through his son or daughter who are minors,22Rambam. However, the Mishnah Berurah 366: 69 says you can be meikil here if necessary. even if they do not eat at his table, because their hand is considered an extension of his own hand.23Therefore they are not making the acquisition, for it is as though he himself were picking up his own bread. But through another minor he may grant ownership rights, (for regarding Rabbinical ordinances, a minor can acquire rights for another person);24See Maseches Gittin 64b, Rambam, Eruvin 1: 20. and, if possible, he should not grant ownership through his wife whom he supports, and not through his son or daughter who are bar or bas mitzvah who eat at his table [i.e. supported by him], for according to some authorities, they too are considered as an extension of his hand.25Since, according to halachah, anything they find belongs to him. However, if there is no other person present, he may grant it through them. If his son is married, although he is supported by his father, all authorities agree that the father may grant ownership rights through him.26Rema 366: 10.
תנא דבי אליהו כל השונה הלכות בכל יום מובטח לו שהוא בן העולם הבא שנאמר הליכות עולם לו אל תקרי הליכות אלא הלכות (נדה ע"ג.)