Shulchan Arukh Orach Chayim · Siman 414

English

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.

English

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.