due to the widespread military use of children in areas where armed conflict and insecurity prevent access by UN officials and other observers, it is difficult to estimate how many children are affected. In 2017, Child Soldiers International estimated that several tens of thousands of children, possibly more than 100,000, were in state- and non-state military organisations around the world, and in 2018 the organisation reported that children were being used to participate in at least 18 armed conflicts. Girls are expected to make up over 40% of the child soldier population. Driving factors Despite children's physical and psychological underdevelopment relative to adults, there are many reasons why state- and non-state military organisations seek them out, and why children themselves are often are drawn to join up of their own volition. Psychological factors Relative to adults, the neurological underdevelopment of children, including adolescent children, renders them more susceptible to recruitment and also more likely to make consequential decisions without due regard to the risks. With these susceptibilities in mind, military marketing to adolescents has been criticised in Germany, the UK, and the US for glamorizing military life while omitting the risks and the loss of fundamental rights. Research in the same three countries finds that recruiters disproportionately target children from poorer backgrounds. In the UK, for example, the army finds it easier to attract child recruits from age 16 than adults from age 18, particularly those from poorer backgrounds. Once recruited, children are easier than adults to indoctrinate and control, and are more motivated than adults to fight for non-monetary incentives such as religion, honour, prestige, revenge, and duty. Social factors In many countries growing populations of young people relative to older generations have made children a cheap and accessible resource for military organisations. In a 2004 study of children in military organisations around the world, Rachel Brett and Irma Specht pointed to a complex of factors that incentivise children to join military organisations, particularly: Background poverty including a lack of civilian education or employment opportunities. The cultural normalization of war. Seeking new friends. Revenge (for example, after seeing friends and relatives killed). Expectations that a "warrior" role provides a rite of passage to maturity. The following testimony from a child recruited by the Cambodian armed forces in the 1990s is typical of many children's motivations for joining up: Military factors Some leaders of armed groups have claimed that children,