We break the middle matzah while it is still covered by its napkin. The larger portion is set aside, to be used as the afikoman. The smaller portion is left between the two remaining matzos, over which the blessing HaMotzi will be recited.

It is customary to break the afikoman into five pieces. If it breaks into six, the sixth piece is placed aside. It is not the prevailing Lubavitch custom for children to “steal” the afikoman. 1

The larger portion is set aside and hidden, to be used as the afikoman

Once one of the Seder guests at the home of the Tzemach Tzedek measured the two pieces of matzah to see which was larger. The Tzemach Tzedek noticed this and commented: “When one must measure to see that a greater one is indeed greater, it is the smaller one which is really the greater.”

The Rebbe Rashab was a small boy at the time. His grandfather’s words made a great impression on him, and from that time onward, he would view with disdain any person whose greatness had to be measured (the Previous Rebbe).2

It is not the prevailing Lubavitch custom for children to “steal” the afikoman

Even stealing of this naturemay have an effect on a child’s personality, ingraining negative tendencies. Therefore, the practice is shunned (the Rebbe). Haggadah Shel Pesach Im Likkutei Taamim.