Genesis 48:9

‘And Joseph said to his father, “They are my two sons whom God has given me here.” And he said, “Bring them I pray to me and I will bless them.” '

Joseph tells him that they are his two sons. His words echo Jacob's mention of them as being born in Egypt. Then, on hearing this, Jacob calls them forward to receive adoption immediately.

“I will bless them.” Or alternately, ‘I will make them kneel.' Some translate ‘take them on my knees', which represents the ‘taking on the knee', the legal rite of adoption. But as he is old and weak, and they are grown men,, he probably takes them, kneeling, between his knees. (Note how Joseph brings them from between his knees - Genesis 48:12). This was thus part of the adoption ceremony.