Wyatt always liked girl's clothes and movies, while his twin brother Jonas played with traditional boy toys.
Born identical twins, the siblings share the same DNA, but their gender identification took divergent paths. Now, at age 14, they are brother and sister, as Wyatt's transition to Nicole is well under way.
Nicole is 5-feet, 1-inch tall and 100 pounds; her twin brother is 5-feet, 6-inches and weighs 115 pounds -- and they are best friends.
Their story -- marked by tearful emotions, bullying at their first school and eventually a lawsuit and a move to a different town -- was chronicled in the Boston Globe on Sunday.
Their parents, Wayne and Kelly Maines, said they brought their transgender daughter into the spotlight in the hopes that their story might shed light on the struggle of others.
"We sat down with our kids at the breakfast table when they were 9 and talked about fear, hate, evil and freedom of speech before sending them to school," their father, Wayne Maines, 52, wrote in an email to ABCNews.com.
"I was very angry and sad to have to talk to our small children in this manner," he said. "We also told them to keep their heads-up, be proud and take care of each other and their friends. I am very proud of them both because they have not forgotten that lesson and they continue to help others whenever it is safe to do so."
Maines, who is director of safety and environmental management at the University of Maine in Orono, said his "biggest concern" was the safety of his son and daughter after the Globe ran its front-page story.
But Nicole said, "The thought of being a boy makes me cringe."
"It is important for people to understand some of the challenges we and other families are dealing with at home, at work and in our communities," Maines wrote, declining to do a full interview.
"We need to watch for a little while to see how this recent step out in the world impacts their safety and ability to function normally at their new school," he said.
He has warned his daughter since she began speaking out before advocacy groups and even at the Maine State House, to watch her back.
A report by the National Center for Transgender Equality and the National Gay and Lesbian Task Force paints a bleak picture of life as a transgender person in the United States. The 2011 survey, "Injustice at Every Turn," found that discrimination is pervasive in "nearly every system and institution."
Transgender youth, in particular, are at disproportionate risk for depression, suicide, substance abuse, HIV and sexually transmitted diseases, according to the Family Acceptance Project at San Francisco State University.
And unlike in the Maines twins, many children do not get the vital support of their own parents and end up homeless.
ABC's "20/20" recently profiled homeless teens, including 13-year-old June, of Portland, Ore., who is transgender. She faced bullying from her brothers and said she feels like an outsider in her own home.