"They feel like their body has gone completely out of control, and I've heard genetic males, who assume a female identity, say please, please, please don't let me grow a beard, like daddy, or a voice like my big brother," Spack said. "They know which physical attributes are going to be absolutely threatening to their entire future ability to blend in."
Of female to male transgenders, Spack said, "The thought of developing breasts is bad enough, but the thought of developing monthly periods is enough to make some of them cut themselves every time they have one."
Doctors are divided over the best way to treat transgender children. Some believe that puberty, despite the extreme distress that accompanies it, is crucial for a child's development and should be allowed to take its natural course.
But a growing number of specialists, including Dr. Spack, believe that early intervention is a better option, and the Grants say that Riley can't wait to undergo this protocol. First, at the onset of puberty, hormone blockers are prescribed to stop the surge of hormones coursing through an adolescent's body.
"It basically puts you at a kind of pre-pubertal state, or in limbo, so to speak. Still growing, but not really maturing in either direction," said Spack, founder of the Gender Management Service Clinic at Children's Hospital of Boston.
A few years later, cross-hormones are taken. For biological males, this means taking estrogen; for biological females, testosterone. These cross-hormones simulate the puberty of the opposite sex. In Riley's case, for example, estrogen will cause her to grow breasts and develop a feminine body shape.
But hormone therapy is expensive and comes with risks. Riley increases her chances of getting breast cancer because of the estrogen. And cross hormones render transgender teenagers sterile.
Then there is the question of if and when to have sex reassignment surgery. "Riley would have it done tomorrow," Stephanie said.
For the Grants, the future is full of questions, while the past seems like a fleeting memory. It's rare that Stephanie allows herself to look at pictures of Riley as a boy. Normally, they are all hidden. She only looks at them when her trans-daughter is not around. If Riley found them, she would destroy them.
Still, the Grants hope that by going public with their private pain, they will help others to comprehend what Riley and other children like her have been through. "I want Riley to have a good life, and for more people to understand the way she is," said Neil Grant.
Stephanie added, "We have to support her, but we don't walk in her shoes. And people who look at her and know her will, I hope, realize what it takes for her to be her every single day."
ABC News' Joneil Adriano and Jennifer Joseph contributed to this report.