Prologue: It is an oddly established custom.
The practice of blessing Jewish boys is to ask Hashem to establish them “K”Efrayim U’K”Menashe” – like Efraim and Menashe. The blessing was established as the norm by none other than Yaakov Aveinu himself. However, unlike the beracha for women who are compared to the matriarchs, why do we select Efraim and Menashe over say – the Avos or the other Shivatim?
Rav Avraham Zalmanis (cited in Chochmas HaMatzpun) notes that in truth, Menashe should have come first in every matter --- as Yosef had attempted – given that he was the rightful Bechor. One must imagine the horror to Menashe when his grandfather Yaakov switched the hands giving Efraim rights over him on all matters. Notwithstanding, Menashe never reacts. Seeing the obvious potential for tension over jealousy that spread between him and Esav and later with his children, Yaakov was amazed and impressed with Menashe’s acceptance. Accordingly, he directed his children to offer the Beracha of Efraim and Menashe – a hope and prayer that no matter where the Jewish family is to reside, that they do so with love, respect and admiration and without room for jealousy that can break them apart.
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Bless the Children
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The Sefer Ma’Avar Yabok notes that one should bless his sons and daughters on Friday night. Three reasons are offered for this practice: Firstly, the power of the Satan is diminished at that time and, as a result, cannot utilize the blessing in a negative manner. Additionally, the Tzinoros (pipes) of bountiful blessing are open at that time and as such make it opportune for Beracha. Finally, it is noted that fathers can sometimes become frustrated with their children and (God forbid) curse them. Offering the Beracha first, can offset any potential Klala (curse) and prevent it from taking effect.
The Sefer Ometz Yosef (79) adds a fourth reason for the practice. He notes that the timing of offering the Berachos – namely after one has spent quality time involved in Tefillah – as on Friday night and Shabbos – one is better prepared to be a conduit for spirituality.
Rav Yaakov Emden (Siddur Beis Yaakov) notes that based on the above it is a Minhag Yisroel to bless the children by placing one’s hands similar to the way that Kohanim bring us the Birkas Kohanim in the Beis HaMikdash.
The problem with the custom is that the Tosafos (Shabbos 118b) note clearly that there is an Issur Aseh (a prohibition) for a non-Kohein to lift his hands in blessing. How then, can a parent bless his child on Friday nights in the format similar to that of the Kohein?
The Mogen Avraham (O.C. 128:1) notes that while it is obligatory for a Kohein to bless the people, a Yisroel may offer Berachos to others as a Reshus. Accordingly, one would not be allowed to make a beracha prior to giving one’s children a Beracha as the Kohanim do prior to Birkas Kohanim. To do so, says the Mogen Avraham, would be to offer Shem Shomayim L’Battala. However, the offering of actual Berachos would be permitted.
The Noda B”Yehuda (Kama, O.C. 6) has difficulty with this explanation. He is concerned lest the reference to the Mogen Avraham’s conerns about Shem Shomayim L’Battala be in regard to the recitation of Hashem’s name while saying the Possukim of Yivareichicha etc. As such, he seems to indicate that one NOT offer these blessing to children unless he is a Kohein.
Rav Ovadiah Yosef (Shut Yabia Omer III:O.C. 14:8) takes exception to this concern of the Noda B”Yehuda. For as he notes, the words of Birkas Kohanim are also Possukim in the Torah. Perhaps one is not OBLIGATED to recite these Possukim but he certainly is PERMITTED to do so and not be concerned about Shem Shomayim L’Battala. Moreover, Shut Kappei Aharon (64) notes that even the Noda B”Yehuda would agree that when parents bless children there is no concern since Hashem wants us to bless one another.
The Bach (O.C. 128) notes that the only prohibition is when one tries to offer the blessing mimicking a Kohein. Mishna Berurah (128:30) adds that when one intends to be like a Kohein, his actions are prohibited (See also Shut Ksav Sofer O.C. 14). Still further, Rabbi Yehoshua Falk (Pnei Yehoshua Kesubos, 24b) notes that only when one does so in the Beis HaMikdash is his action prohibited as it attempts to mimic the Kohein’s.
Based on the above, the Torah Temimah (Bamidbar 6:23:131) cites the Vilna Gaon who felt that one should not bless the children with 2 hands as the Kohein does. The Siddur Ari concurs. Others disagree and note that there is no issur (Shut Yichaveh Daas V:14) or perhaps even an obligation (Siddur Rav Yaakov Emden) to bless the children with 2 hands on the head. The argument is that it is clear to all that the parent is not stepping in to fill the role of the Kohein.