The source for blessing one’s children is in Parshat Vayechi, in the verses that describe Jacob blessing Joseph’s children, Ephraim and Manasseh.
The pasuk explicitly says that one should use the names of Ephraim and Manasseh when blessing sons, but offers no accompanying explanation.
Rabbi Dunner examines the sources, and presents a comprehensive overview of this ancient ritual, looking at the meaning of the blessing itself, as well as the customs that surround the actual moment when one blesses one’s child.
This shiur was sponsored by Mrs. Chavi Hertz in memory of her father, Yisroel David Mikel z”l, whose yahrtzeit is on 9 Tevet.