The report put the increase down to the “proliferation of incidents of armed violence, the perpetuation of long-running conflicts and the increasingly urban character of armed violence”.
The report launched as military commanders and defence ministers, including the UK Defence Secretary Gavin Williamson, met at the Munich Security Conference.
Save the Children chief executive Kevin Watkins said: “The Munich Security Conference is an important event in the security calendar and the fact that the protection of children in conflict doesn’t even figure on its agenda, and never has done, is an illustration of the complacency we’re dealing with.”
He said that representatives from Saudi Arabia, whose bombs have been pounding Yemen, would be at the conference but they faced no sanction from the international community.
Mr Watkins added that the UK had a strategy on protecting civilians but it has not been updated since 2010.
“The word children hardly figures in that entire document and there’s no reference to what the UK could be doing to hold accountable people who are committing war crimes and even potential genocide,” he said.