Yesimcha Elokim k'Efraim v'chMenashe

Why is the bracha we give to our children is that they should become like Efraim and Menashe? It could have been a myriad of other things, so what is notable about them that they were able to inherit from Yakov a portion equivalent to the previous generation, their uncles?

My Zaide explains that Menashe and Efraim were worthy of being considered Yakov's own children and two of the 12 Tribes, and this is because of their being born and raised in Egypt. It is not such a blessing to say that they should become like Reuven, Shimon etc, as they were raised in Yakov's house; it's not so much a big deal to tread the path you're already on, but the fact that 2 boys, born in Egypt, to a father who was the viceroy of Egypt who had left his heritage at 17 (and we could understand if he'd sought to cut off ties with his past, the past that he'd been cut out of by his brothers), that is a massive chiddush, that people can rise from the 49th level of tuma and become one of the Shivtei Ka. This is truly inspirational, that each of us has unlimited potential. This is the blessing we give our children, that they should transcend all obstacles, just like Efraim and Menashe.

D explains this alternately, that Yaakov switched hands, and said that the younger son would become greater. Not a peep was uttered by either, and Yaakov blessed them. There was not a hint of jealousy or animosity to the other, they were content for their lot, and Menashe was happy for Ephraim to get what should have been his. And there was no gloating on Ephraim's part, there was merely acceptance. D explains that the blessing we give to our children is that they should have this relationship with each other (which perhaps leads on to what my Zaide says?).