Siman 414
Presented here for study, not as a practical ruling. The Shulchan Aruch rules by Sephardi custom, the Rema's glosses by Ashkenazi custom, and the Kitzur follows Ashkenazi custom. For a practical question, ask your rabbi.
א אֵין מְעָרְבִין עֵרוּבֵי תְּחוּמִין לְאָדָם אֶלָּא לְדַעְתּוֹ, שֶׁמָּא אֵינוֹ רוֹצֶה לְעָרֵב בְּאוֹתוֹ רוּחַ שֶׁרָצָה זֶה; חוּץ מִבְּנוֹ וּבִתּוֹ הַקְּטַנִּים אֲפִלּוּ אֵינָם סְמוּכִין עַל שֻׁלְחָנוֹ וְעַבְדּוֹ וְשִׁפְחָתוֹ הַכְּנַעֲנִים. וַאֲפִלּוּ מִחוּ בּוֹ שֶׁלֹּא לְעָרֵב עָלָיו, וַאֲפִלּוּ עֵרְבוּ הֵם עֵרוּב אַחֵר, אֵינוֹ כְּלוּם. אֲבָל בְּנוֹ וּבִתּוֹ הַגְּדוֹלִים אֲפִלּוּ סְמוּכִים עַל שֻׁלְחָנוֹ, וְעַבְדּוֹ וְשִׁפְחָתוֹ הָעִבְרִים וְאִשְׁתּוֹ, אֵינוֹ מְעָרֵב עֲלֵיהֶם אֶלָּא מִדַּעְתָּם. וְאִם עֵרֵב עֲלֵיהֶם וְשָׁמְעוּ וְשָׁתְקוּ וְלֹא מִחוּ, יוֹצְאִים בְּעֵרוּבוֹ. אֲבָל אִם מִחוּ בּוֹ אוֹ שֶׁעֵרְבוּ הֵם עֵרוּב אַחֵר לְעַצְמָם, אֵין עֵרוּבוֹ עֵרוּב לָהֶם.
1 That one may only make an eruv with someone's knowledge. Contains 2 sections One may not make an eruv of boundaries for a person without his knowledge, since perhaps he does not wish to make an eruv in the direction this one chose — except for his minor son and daughter even if they do not eat at his table, and his Canaanite manservant and maidservant, even if they protested against making the eruv for them and even if they made another eruv themselves, it is void. But for his adult son and daughter even if they eat at his table, his Hebrew manservant and maidservant, and his wife — he may only make an eruv with their knowledge. If he made an eruv for them and they heard and were silent and did not protest, they may use his eruv. But if they protested or made another eruv for themselves, his eruv is not valid for them.
ב קָטָן בֶּן שֵׁשׁ שָׁנִים אוֹ פָּחוֹת, יוֹצֵא בְּעֵרוּב אִמּוֹ וְאֵין צָרִיךְ לְהַנִּיחַ עָלָיו מְזוֹן ב' סְעֻדּוֹת לְעַצְמוֹ.
2 A child of six years or younger goes out by virtue of his mother's eruv, and one need not place two meals' worth of food for him separately.