The children were killed after being caught in the crossfire of a gun battle that followed the blast on Sunday, a US occupation military spokesman said.
The spokesman said it was not possible to establish how many civilians had died as other Iraqis rapidly removed the bodies.
"One of our Task Force Baghdad soldiers was killed and three others were wounded as a result of an improvised explosive device explosion," said Lieutenant-Colonel James Hutton, spokesman for the US Army's 1st Cavalry Division.
He said occupation troops who later sought to recover the Humvee vehicle damaged in the blast returned fire after being targeted from rooftops.
"The soldiers then received fire from rooftops and returned fire. The children moved back to the Humvee"
US occupation military
"Civilians, apparently including children, were caught in the crossfire," the spokesman said.
He said the first group of soldiers was travelling in a convoy in Baghdad when the roadside bomb blew up. The dead and wounded were swiftly evacuated.
When other troops arrived to recover the Humvee, children were inside the vehicle, looting parts, said Hutton, adding that they dispersed as the soldiers arrived.
"The soldiers then received fire from rooftops and returned fire. The children moved back to the Humvee," he said, indicating that was the point at which they were caught in the crossfire.