Mental health professionals disagree that a six year old has even found a sexual identity. It’s great that your child is now doing much better, but even the child’s goal is impossible. There is no way to use the male body to gestate a baby. That’s specifically the role that the other type of body is for.
Perhaps the child needs not so much rights, as the protection of adults who see the longer arc, what the stages of development are, what is and isn’t possible, and the poor mental health outcomes for those who undergo surgical transition. For example, Jenner is thinking of going back to being Bruce and is the rare person with the resources to make that choice twice.