Girls account for 23% of all trafficking victims detected globally, according to the 2018 Global Report on Trafficking in Persons
, produced by the UN Office of Drugs and Crime (UNODC).
The figure, which is based on data from 2016, is up from 21% in 2014, and 10% in 2004, the year when the UNODC began collecting data on children.
Boys account for 7% of reported trafficking victims, down from 8% in 2014, and up from 3% in 2004.
"In the profile of identified victims, we are seeing more and more children, an increase particularly in girls," says Angela Me, chief of the UNODC's research and trend analysis branch.
But the UN says that this rise could be due to better detection of victims globally.
Me explains that trafficked girls are typically victims of sexual exploitation, while boys are more often exploited for forced labor.
The UN defines girls and boys as being aged less than 18, but Me says some member states use different definitions.
The report shows that women and girls account for almost three quarters of all detected victims of trafficking in 2016. Females make up 94% of the total victims trafficked for sexual exploitation, and 35% of those trafficked for forced labor.
It also finds that armed conflict in some regions of Africa, the Middle East and Asia is likely to increase vulnerability to trafficking.
It says that areas with weak rule of law and lack of resources provide traffickers with "fertile terrain" to carry out operations, adding that armed groups take advantage of people in a desperate situation to traffic victims for sexual exploitation, forced marriage, armed combat and various forms of forced labor.
Populations fleeing conflict, such as Syrian, Iraqi and Rohingya refugees are also targeted by traffickers.
"In migration flows, you have a dispersion of families and then you have many children who travel alone, who definitely become more vulnerable to be trapped into exploitative situations," says Me.
The report also indicates that the overall number of reported trafficking victims has increased. In 2016, about 40% more victims were detected compared to 2011.
But the UN says that this rise could be due to an increase in trafficking globally, or it could be a result of enhanced national capacities to detect, record and report data on trafficking.
In 2009, only 26 countries had an institution which systematically collected data on trafficking cases, whereas in 2018, the number had risen to 65.
"There are now a whole bunch of countries that have new legislation so are more equipped from a legislative point of view to criminalize and to prosecute and at the same time to protect the victims," says Me.