Halacha Orach Chaim 186

Children should be taught to recite Birchas Hamazon. Reb Shlomo Zalman Aurbach rules that a child, who eats less than the necessary amount required for Birchas Hamazon, should be taught to bench if he is full from the meal. The reason for this is because the Pri Megadim is of the opinion that one has a Torah obligation to recite Birchas Hamazon if he is full, even if the necessary amount was not eaten.

If the child is not full from such a meal, he should not recite Birchas Hamazon.

We learned in our last post, that one can recite a Bracha for others only if the level of obligation for the one reciting the Bracha is equal or greater than the one listening. Based on this rule, the Kaf Hachaim writes that a child may recite Birchas Hamazon for other children, as their obligation is equal.

As a side note, the Mishna Berura in Simun 60 writes that an adult can only fulfill an obligation when singing Birchas Hamazon with children if the adult has specific intention for the Mitzva. This is because Mitzvos need Kavanah – proper intent. If an adult is lacking proper Kavanah when Benching alone, we rule that Benching does not need to be repeated because Benching itself is assumed to be for the Mitzva, and is therefore viewed as proper intent. However, when Benching with children we assume the intent is to teach and not for the Mitzvah.