About 75% of the estimated 345 violent deaths that occur daily happen in countries at peace, the report said.
"We are uncovering the fact that children experience extreme violence in everyday life, everywhere," Susan Bissell, global head of child protection for UNICEF told the Thomson Reuters Foundation.
In some countries, deaths from violence are rolling back gains made in preventing childhood deaths from disease or hunger.
"What is shocking is that we have for two or three decades focused a lot, and importantly, on child mortality from preventable diseases, and what this report says is that we need to be thinking about child mortality from all causes," Bissell said.
"And it's shocking to imagine that we might not achieve our goals in terms of child survival if we don't address the protection of children. These go hand in hand," she added.
In Brazil, the number of children dying from preventable disease before the age of five has dropped since 2000, but almost 15,000 lives have been lost to violence in adolescence, said Leah Kreitzman, head of campaigns and advocacy for UNICEF UK.
Millions of children are vulnerable to physical, sexual and emotional abuse in their homes, schools and communities.
"If you scratch beneath the surface, the statistics around things like sexual violence, violent discipline in the home and the school, all of these things make it very difficult for children to develop," Kreitzman said.
"Children are getting their mental and physical health permanently damaged by violence every day," she added. But many families do not bother going to the authorities because they know they will not get help, Kreitzman said.
In Kenya, one in three girls and one in six boys experience sexual violence. But just 1% of cases of sexual abuse are recorded by the police.
"If people know that they can act with impunity then they can continue being violent to children," she said.
Protecting children in war zones
War amplifies and magnifies the violence that children normally experience every day. Where there is a pejorative view of girls and boys, or where there is impunity and no rule of law, it simply becomes worse for children when war breaks out, Bissell said.
Education can help protect children in many conflicts. It gives children a sense of normality, but also can protect them from being recruited by armed groups.
Thomas Lubanga, who has been imprisoned by the International Criminal Court for using children to fight in his rebel group in Congo, recruited many of them in communities without a functioning school or health service, Bissell said.
"There's no silver bullet but for UNICEF education is a huge intervention which we know yields results," she added. The education system itself is under attack in many countries. Schools and universities have been attacked by armed groups in at least 70 countries over the past five years.
"The attempted murder of Malala Yousafzai in Pakistan, and the kidnapping of 276 Nigerian girls by Boko Haram, has finally woken the world up to the struggle that children face from those who will kill to stop them receiving an education," the UNICEF report said.
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