The Torah tells us that when Yaakov Avinu blessed his grandchildren Ephraim and Menasheh, he said that in the future, whenever Jewish parents bless their sons, they should say, "may Hashem make you be like Ephraim and Menasheh" (בראשית מ"ח:כ'). Many people follow the custom that the parent blesses his children on Friday night (and prior to Yom Kippur), and the blessing includes the request that one's own sons should be like Ephraim and Menasheh. The question is, why are our sons compared specifically to the sons of Yosef? Why not compare them to other great Jewish figures? Some suggest that this is because within Yaakov's entire family, these two were the only two sons born into Golus, meaning that they were the only ones born away from the rest of the family and outside of Eretz Yisrael. But despite all the corrupting temptations that Golus has, they nevertheless followed Hashem's ways as well as Yaakov himself did. Therefore, when parents bless their sons on Friday night, they pray that these sons should be like Ephraim and Menasheh, able, if necessary, to withstand all temptations and stick to Hashem's way. They ask Hashem to protect their son(s) from the horrors of Golus and to help them stay on the path of Hashem.
Another trait which identified both Ephraim and Menasheh was their lack of envy towards each other. Even though Ephraim was younger than Menasheh and Ephraim received a greater blessing than Menasheh, as Yaakov states clearly (שם פסוק י"ט), they saw no reason to envy each other. They knew that if they envied each other, it would break them apart and eventually split their entire nation. Instead, each was content with his own role and recognized his own place. Hatred amongst the Jews can cause only the downfall of the people. It is when the Jews are united and are like Ephraim and Menasheh that they will thrive and bring credit to Hashem and His Torah. This, then, may be another reason why we ask that our sons should be like Ephraim and Menasheh. Although it is natural for there to be sibling rivalry, we ask Hashem that ultimately, all members of the family should get along and work together on a common goal.