The aliens should be allowed to extend to human infants the invitation to leave their parents to join the alien civilization. As I understand it, this would result in every human infant leaving their parents, but that would indeed be the correct rational choice when one has the preferences that human infants have.

So every human infant would leave their parents, and it would be ethically correct to allow this. If humans want to reproduce in a way where their children don't immediately leave them, they should modify their reproduction techniques to produce children with preferences that allow such an outcome. (Or just start constructing new additions to the human race as adults to begin with, instead of producing children.)