The Torah portion Vayehi comprises the last months in the life of Jacob, his death in Egypt, and his burial in the Land of Israel.
During Jacob’s final illness, Joseph brings his sons Ephraim and Manasseh—Jacob’s grandsons—to him, and Jacob effectively adopts them as his own sons. This explains why the Twelve Tribes of Israel include separate tribes of Ephraim and Manasseh, but no tribe of Joseph. Jacob also blesses his [grand]sons with the words, “By you shall Israel invoke blessings, saying: God make you like Ephraim and Manasseh.”
This blessing—God make you like Ephraim and Manasseh—is the traditional blessing for parents to bestow upon their sons on erev Shabbat. The blessing for daughters asks that they be like Sarah, Rebecca, Rachel, and Leah.
In family workshops, I like to encourage parents to bless their children on Shabbat, because it provides an opportunity to transmit values to children.
Once children have started Sunday school, they are likely to recognize the names Sarah, Rebecca, Rachel, and Leah, even if they cannot fully recount their stories. Young children today, however, may not recognize the names Ephraim and Manasseh, and the traditional blessing may therefore be less meaningful.
One of my friends, certain that her son, then four years old, would not recognize Ephraim and Manasseh, would substitute other names from the Torah that she thought he might remember. Occasionally this was incongruous: traditional Jewish parents did not wish their child to grow up to be like Esau (although Esau does represent some qualities that the modern world values). Be careful what you wish for!
Because young children think in concrete terms, it may be helpful to express a Shabbat blessing through references to real people whom they know, and to be explicit about the qualities you hope they will develop. For example, although a midrash considers Jacob (yes, the same Jacob) the archetype of the Jewish scholar, rather than citing Jacob as a model, you might say, “May God help you to become a good student like Grandpa Al was,” or “to have a sense of humor like Aunt Debbie.”
Another reason for blessing children on Shabbat is that parents who may have some difficulty with prayer in general usually find it easier to express prayerful wishes for their children. The traditional time for blessing children is immediately after lighting the Shabbat candles. Place your hands on the children’s heads as you state your hopes for them, citing either the persons you choose or Ephraim and Manasseh/Sarah, Rebecca, Rachel, and Leah. Conclude with the priestly blessing: “May the Lord bless you and guard you, May the Lord show you favor and be gracious to you. May the Lord show you kindness and grant you peace.”