Insights into Birkat Habanim Custom

One of the earliest mentions of the custom to bless the children on Friday night appears in the Siddur Beis Yaakov of Rav Yaakov Emden (Altona, 1745).

He writes, that it is the custom of the people of Israel to bless their children on Friday night after evening prayer services or as they enter their home upon returning from shul. With the onset of Shabbos, shefa, loosely translated as Divine blessing, is abound and by blessing our children we are able to grab hold of that free flowing Divine grace and pass it on to our children which in turn allows for the blessing to multiply manifold times.  Children are the best receptacles of this shefa because they are uncontaminated by sin and therefore serve as purer conduits of the shefa.  However, he adds, one should still bless their older children as well.

When conferring the blessing one should place both hands upon the child's head as Moshe Rabeinu did when he blessed Yehoshua and transferred the mantle of leadership to him.  Blessing with both hands demonstrates a wholeheartedness in your desire to bless the other person.  This is the reason the kohanim bless us with two hands and our Rabbis tell us that angels bless man with two hands on Friday night as well. Although we are provided with the standard text for blessing our children on Friday night, Rav Emden notes one is allowed to add his own personal blessing in whatever language he desires.