Blessing children on Friday night:

It is an old age custom for parents and Rabbis to bless their children and students with Birchas Kohanim on Friday night.^[1] Doing so does not transgress the prohibition^[2] against a non-Kohen reciting Birchas Kohanim^[3], although it is forbidden for the person to raise his hands like a Kohen upon doing so, and he also may not intend to perform the Mitzvah of Birchas Kohanim upon doing so.^[4] The blessing may be said with Hashem’s name.^[5] The blessing is given after Maariv or upon coming home from Shul. The reason for this is because on Shabbos, there is a special holiness that resides on the hands which can be transferred onto the children and students.^[6] Some^[7] are no longer accustomed to bless the children on Friday nights and rather do so only on special occasions, such as Yom Kippur and the day of the wedding, and so is the widespread Chabad custom.^[8]

Placing the hands on the person’s head: Due to the above prohibition against lifting the hands while saying Birchas Kohanim, some^[9] are accustomed not to even rest both hands on the head of the person being blessed when blessing him with Birchas Kohanim, and rather rest only one hand on his head. Other Poskim^[10] rule it is permitted and encouraged for one to do so. Practically, the widespread custom is to be lenient and allow the placing of two hands on the head of the person being blessed^[11], and so was the custom of the Chacham Tzevi^[12] and Rebbe Rashab on Erev Yom Kippur.^[13]

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[1] Sefer Hachaim [brother of Maharl] 3/6; Maavor Yabok Sifsei Renanos 43; Siddur Yaavetz; Pela Yoeitz Brachos; Kaf Hachaim 262/17; See Piskeiy Teshuvos 271/1

[2] See Admur 128/2; Rama 128/1; Kesubos 24b

[3] See Bach 128; M”B 128/3; Kaf Hachaim 128/39; Biur Halacha 128/1 “Viein Lezar”

[4] See Poskim in previous footnote

[5] See Mahariy Assad O.C. 41; Keren Ledavid; Kapei Ahron 64

Some Poskim rule it is forbidden to say Hashem’s name in the blessing due to it being in vain. [Noda Beyehuda Kama 6]

[6] Siddur Yaavetz ibid; Kaf hachaim ibid

[7] Makor Chaim of CHavos Yair 270; Menachem Tziyon in name of Rimnavor in Derushim Lipesach that he would only do so on special occasions and not every Shabbos; This custom is not recorded in the writings of the Arizal

[8] Rabbi Leibal Groner replied to my question as to what is the Chabad custom: “In majority of instances I did not hear of or witness this custom in Chabad homes, however there were some Chabad families I knew of who did follow this custom.”

[9] Custom of Gr”a, brought in Torah Temima Bamidbar 6/23; Siddur Reb Shabsi; Maavor Yabok Sisei Renanos 43; See Piskeiy Teshuvos 128/6

[10] Siddur Yaavetz Seder Leil Shabbos; Sheilas Yaavetz 2/15 that so was the custom of his father the Chacham Tzevi

[11] See Daas Sofer 1/14; Beir Moshe 4/25; Tzitz Eliezer 11/8; Yechaveh Daas 5/14

[12] Brought in Sheilas Yaavetz ibid

[13] Otzer Minhagei Chabad p. 194