Secret adoptions should the child know they are adopted?

My uncle and aunts are in the process of adopting a baby. The whole family knows they are adopting but they have already voiced to everyone that they don’t want the child to know. They plan to raise the child with the child believing they are biologically theirs and not knowing she’s adopted. Of course I will go along with this and will never say anything to the child about adoption. But morally do you think a child has a right to know they are adopted? Or is this for the adoptive parents to decide?