If I thought that parents have a right to authorize the killing of an embryo/tiny unborn human to benefit their own child, then I would also logically have to approve of killing an already born human to "harvest" the heart, lungs or kidneys because it will benefit someone else.
If you don't see the logic, you have serious moral blindness.
Everyone has the God given rights to life, liberty, and the pursuit of happiness. Killing someone to utilize the murdered person's resources deprives him/her of all three.
If you think an unborn tiny human aka embryo is not human, what the hell is it?
I see a group of cells as a group of cells, as do a lot of people. I'll ask again - would you agree that it's the right of the parents concerned to make their own mind up whether or not to have this treatment if it proves effective?