In a report, the UK's branch of the UN children's agency Unicef says most of those deaths occur outside war zones.
It says millions of young people under the age of 20 feel unsafe in their homes, schools and communities.
It also blames rapid urbanisation, youth unemployment and rising inequality for creating greater risks.
Unicef UK says it published its report - Children in Danger: Act to End Violence against Children - to mark the launch of the Children in Danger campaign.
It warns that about 345 children under 20 could die from violence each day in the next year unless governments around the world take action.
The document's findings suggest that children who are victims of violence have brain activity similar to soldiers exposed to combat and more than 30% of them are likely to develop long-lasting symptoms of post-traumatic stress disorder.
It says those living in poverty are more likely to be the victims of violence. An adolescent boy in Latin America is 70 times more likely to be murdered than one in the UK.
"We want children living in fear to have a chance of feeling safe and secure," Unicef UK's executive director David Bull said.
"A global target would galvanise action to make the world safer for children."
Only 41 countries, Unicef UK says, have an explicit ban on violence against children.
But the report says that there is no room for complacency in richer countries as no nation is currently able to provide children with the full protection they need.
A child is killed by violence every five minutes in the world, a leading charity says, calling for new targets to end all forms of abuse by 2030.