Joseph has two children: Menasheh, the older, and Ephraim, the younger. Jacob blesses them both before he dies. He tells Joseph that, although the descendants of Menasheh will become a great people, the descendants of Ephraim will be even greater. In fact, King David was from the tribe of Ephraim.
Jacob says to Joseph: Israel will use your sons' names to bless their own children. They will say: "God make you like Ephraim and Menasheh." Do your parents place their hands on your head and bless you on Friday night? If they do, that is what they say. (If you are a girl, they say: "May God make you like Sarah, Rebecca, Rachel and Leah.)
Why did Jacob instruct our parents to use Menasheh's and Ephraim's names? The answer is simple: Menasheh and Ephraim did not fight. Cain killed his younger brother Abel; Esau wanted to kill Jacob; Joseph's 11 brothers wanted to kill him. But, even though Ephraim got the blessing Menasheh should have received, they remained peaceful and loving brothers. And that is what all parents wish for their children.