The US is giving hundreds of millions of dollars in military aid to countries that use and recruit child soldiers.
Human Rights Watch (HRW) on Thursday condemned the practice, and urged the Obama administration to review its spending.
The call came following the release of a new list of countries implicated in the use of child soldiers by the US State Department.
The list of 10 countries includes Burma, the Democratic Republic of Congo, Iraq, Nigeria, Rwanda, Somalia, South Sudan, Sudan, Syria, and Yemen.
"Many of the governments listed by the State Department receive US military aid year after year despite their continued use of children as soldiers," said Jo Becker, children's rights advocacy director at HRW.
"President Obama should make clear that countries using child soldiers are going to lose US military support."
The omission of Afghanistan from the list led HRW to accuse the US government of turning "a blind eye" to the abuse of children in the country.
The organisation said there was evidence that the Afghan Local Police, a government-backed militia engaged in combat operations against the Taliban and other insurgents, recruits and uses child soldiers.
Becker said the US has spent hundreds of millions of dollars to support the force, and insisted that Afghanistan should be "subject to military sanction".
"The Afghan government has failed to rein in the militia's recruitment of children while the US turns a blind eye," she added.
Though the 2008 Child Soldiers Prevention Act forbids certain forms of US military assistance to countries involved in the practise of recruiting and using child soldiers, the President can waive this prohibition for national security reasons, HRW said.
Last year, Obama initiated full or partial waivers to four of the five listed countries. Since 2010, waivers have been issued in 26 of 33 cases.
"President Obama should take a much harder line, and insist that countries that receive US military aid end their use of child soldiers," Becker said.
"Unconditional military aid sends a terrible message that the US knowingly supports countries that use children to fight."
Around a quarter of a million children around the world are soldiers, and though many are recruited by rebel groups, thousands are part of official government forces. UK charity War Child estimates that 40 per cent of all child soldiers are girls who are regularly subjected to sexual abuse.
