How many children and teenage girls are ready for marriage? Yet the practice is shockingly prevalent: One out of nine girls in developing countries will be married by age 15, according to the United Nations. An estimated 14.2 million girls a year will become child brides by 2020 if nothing changes.

Driven largely by poverty and cultural traditions, such marriages are usually arranged by family members. The physical and emotional consequences can be life shattering, even fatal.

Pulitzer Prize-winning photographer Stephanie Sinclair has been documenting child marriage all over the world for more than a decade. Her work, which was featured in a National Geographic magazine feature in 2011, has raised awareness and helped educate both citizens and world leaders. She spoke to us after attending a recent United Nations' Commission on the Status of Women (CSW) event focused on addressing the problem of child marriage. (Pictures: The secret world of child brides.)

What do you find most disturbing about child marriage?

I think the thing that we must acknowledge is that in most cases these young children do not want to be married. They want normal lives. They want to play with their friends, they want to be educated, and they want to have a full adolescence. These marriages rob many girls of their innocence, many times before puberty, and this is something that as a global society we cannot tolerate. The bottom line is that child marriage isn't just harmful to the girls involved. It's at the root of so many other societal ills: poverty, disease, maternal mortality, infant mortality, violence against women. All of those are symptoms connected to the same problem. If you solve the child marriage problem, these other issues benefit as well. And as the speaker at last week's CSW event put it: Let's be honest, when an eight-year-old has sex with a 20-something-year old, that's rape. It is child rape. It's something we cannot be okay with.

What's changed, if anything, since the NGM story ran in 2011? Have efforts to stop child marriage gained force?

When we did the story, there was not the same kind of public awareness of child marriage that there is now. But shortly afterward The Elders, a group of world leaders dedicated to peace and human rights, made it a priority issue and formed Girls Not Brides, which now has over 200 members based throughout Africa, South Asia, the Middle East, Europe, and North America—all united by a commitment to end child marriage and enable girls to fulfill their potential.

My photo agency, VII, has also since partnered with the United Nations Population Fund (UNFPA) for a two-year campaign on the topic, which kicked off with a huge exhibition at the UN headquarters in New York City on October 11, 2012, the first-ever International Day of the Girl Child. My photographs were featured throughout the UNFPA report released that day, titled "Marrying Too Young." As part of the two year campaign, I am continuing to produce new work on the issue with colleague and filmmaker Jessica Dimmock. The campaign has an active blog and website, tooyoungtowed.org, where will be publishing additional stories and updates about where the exhibition will be traveling worldwide.

What more can be done?

A multifaceted approach is needed to address the issue of child marriage. Education is still the single most protective factor. This means keeping the children in school as long as possible, as well as educating the communities about the harmful impact of child marriage on the health of their girls, their grandchildren, and their societies as a whole. I also strongly believe there is not just a need for awareness-raising and prevention work, but we must also find ways to help the girls who are already in these marriages, be it through giving financial incentives to their families to let them stay in school, or vocational training so they can have more say in their lives and households. Quality medical treatment is also needed for girls who are giving birth at young ages. These girls need long-term solutions.

Unfortunately, there is no quick fix. But there seems to be a growing movement aimed at ending child marriage. A few months ago, former Secretary of State Hillary Clinton announced a United States Agency for International Development (USAID)-sponsored pilot program in Bangladesh that will work with religious leaders, media, local governments, and NGOs to foster community support for an end to child marriage. And Archbishop Desmond Tutu, chairman of The Elders, has announced a very ambitious goal: to end the practice by 2030. If this issue remains a global priority, I'm optimistic that we can meet that deadline. There are always ways to do it. You just have to be creative. A lot of initiatives have started, but it's about keeping the momentum.

How do you plan to continue covering this issue?

My film partner and I just returned from Tanzania and are following a narrative there on the health repercussions for young brides. We return again in about two weeks. We are looking at the issue of fistula, one of many health issues, including uterine prolapse and ruptured uterus, that girls suffer because of child marriage. In fact when I was in Yemen I interviewed a female gynecologist who told me: "When the girls in your country are at the beginning of their lives, the girls in our country are at the end of their lives."

You've heard the personal stories of many child brides. Was there one that especially moved or outraged you?

They are all heartbreaking, but probably the one that got me the most was the little girl Tahani. She was eight when I met her, but six when she was married to her 25-year-old husband in Hajjah, Yemen. She is featured in the video we did that went with the National Geographic story. Even though she looks young—her teeth haven't even grown in yet—there is a matter-of-factness about her that makes her seem older, which is clear evidence of trauma, otherwise she wouldn't be so dissociated talking about her sexual experience at age eight. Serious innocence has been lost. She went to school, she even lived next to a school, but wasn't able to complete her education because once her mother died, there was no one to stand up for her.

Are there any happy endings you can share?

Yes. In 2010, I photographed a Yemeni girl named Nujoud Ali. Nujoud was one of the lucky ones. Due to her own bravery and with the help of a female lawyer named Shada Nasser, Nujoud was able to get a divorce at age 10, just a few months after her marriage. She is now having a second chance at life. We can only hope that other girls will get the support they need should they want to take the same steps.