The football explosion happened in a village in the mountains of Lower Dir. The children, five of them girls, found the ball as they were returning from school. Seven victims belonged to the same family.
Pakistan's Interior Ministry chief, Rehman Malik, blamed the Taliban saying: "The Taliban have exposed their real face by killing innocent children."
He said investigators would check whether the children were targeted because their families had refused to let the Taliban take them for training, including as suicide attackers.
He also appealed to parents across North West Frontier Province (NWFP) to stop children accepting food or toys from strangers.
And they say that American airstrikes drive civilians into the arms of the Taliban? Anyone who seeks the shelter of their embrace deserves whatever they get.