Gen. Joseph Dunford, commander of the International Security Assistance Force, said NATO forces Thursday mistook the children for insurgents and fired at them from the air.
"I offer my personal apology and condolences to the family of the boys who were killed," Dunford, said. "I am committed to ensuring we do the right thing for the families of those we harmed, as well as for the community in which they lived. We take full responsibility for this tragedy."
He pledged NATO forces would do everything possible to prevent Thursday's mistake from happening again.
The shooting took place in Shahid-e Hasas district, Uruzgan province, in central Afghanistan.