The world can be a dark place for many children: the "lost boys" from Sudan, refugees fleeing the conflict in Syria, child sex workers in Brazil, baby girls abandoned in China, kids pulled into gang drug wars in the United States.

Such suffering by children is more common than most people might think and represents what some believe to be one of our biggest public-health crises of all time. A study published in January in the journal Pediatrics puts that violence into stark perspective by estimating that as many as half of the world's 2 billion children experienced physical, sexual or emotional violence in the previous year.

The trauma can inflict a physical toll as well as a psychological one. Research conducted by the U.S. Centers for Disease Control and Prevention and Kaiser Permanente in 1995 and 1997 found that those who experience violence in childhood are at higher risk as adults for a diverse range of conditions including cancer, diabetes and obesity.

Despite growing recognition of the problem, however, efforts to fight it have been unfocused with no global agreement about the right approach — until now.

On Tuesday, the World Health Organization announced the first coordinated plan to end violence against children. It includes a seven-point strategy that consists of many practical measures, such as implementing and enforcing laws that limit young people's access to firearms; changing beliefs and values around gender roles, which would presumably target countries where girls have fewer rights and less freedom; creating safe environments by doing things like improving housing; increasing parent and caregiver support; strengthening economies; shoring up support services such as treatment programs for juvenile offenders; and educating children in life and social skills.

The plan being adopted by the WHO and partner organizations (including UNICEF, USAID and the World Bank) is pioneered by the CDC and originated through its work in other areas. One of the first studies that put violence against children on the map for the public health agency was the Adverse Childhood Experiences study. Published in the American Journal of Preventive Medicine in 1998, it found that childhood abuse and household dysfunction were linked to many of the leading causes of death in adults.

The issue came up again in a big way for the CDC through its work on the spread of HIV/AIDS. Researchers found that in some countries in Africa and Asia, sexual abuse of children drives the HIV epidemic.

In 2015, the CDC published another important study on violence and children focusing on seven countries: Swaziland, Tanzania, Kenya, Zimbabwe, Malawi, Haiti and Cambodia. The Violence Against Children Surveys turned up shocking numbers. Between 2007 and 2013, at least 1 in 4 females and 1 in 10 males in those countries experienced some form of childhood sexual violence, and few of them received health care, legal assistance or counseling.

The issue of violence against children is a personal one for CDC Director Tom Frieden. Before he took over the CDC in 2009, he served as the commissioner of the New York City Department of Health and Mental Hygiene. During his time there, his wife ran a battered women's shelter for 15 years, and he met many of the women and their children who sought help at the shelter. Many of the children he met had been abused themselves and were in mental and physical pain.

"It was a horrific thing to see," he remembered in an interview.

Through his later work at the CDC, Frieden said it was clear that violence against children is a "huge, devastating, pervasive problem." And the experience many children go through is "heartbreakingly consistent" no matter their race, religion or country.

"We look so often at the violent events of the day and they are horrifying and unacceptable. As public-health workers, we try to go upstream and prevent terrible things from happening as early as possible. This is important if we are going to reduce the toll of mental or ill health and the suffering children experience every day around the world," he said.

Frieden said the same types of approaches we've applied to fighting tuberculosis, HIV and Zika could be applied to violence. Instead of focusing on trying to do everything for everyone, he explained, you focus on things that really work. For each of the seven strategies in the new plan, there are numerous interventions that have been tested and deployed.

"We need to be thinking of violence as a contagious disease and interrupt that cycle," he said.

The first step, Frieden said, is to admit there's a problem. The issue of child violence is "sometimes an uncomfortable thing for people to bring up, so they don't bring it up."

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