The generals said some anti-government fighters had also been killed in the strike.
Michael Ryan, a US brigadier general, said that the investigation proved how seriously the US takes civilian casualties.
The US has come under increasing criticism over the past few months over the deaths of civilians in military operations in Afghanistan.
Hamid Karzai, the Afghan president, said that rising civilian deaths was a source of tension between Kabul and Washington.
There are currently 80,000 US and Nato soldiers in Afghanistan, battling Taliban and al-Qaeda fighters.
Barack Obama, the US president, announced last week that an additional 17,000 troops would be sent to the country, in addition to the 38,000 already stationed there.