At least one more child was also injured in the blast, interior ministry spokesman Najib Danish said, adding that all victims were members of the same family.
He said two rockets had been launched from an unknown location in Kabul this morning. "One hit a residential house causing casualties, the second hit a cesspool, with no casualties," he said.
"Police teams have been deployed looking for possible location and perpetrators of the attack."
A UN report earlier this year showed that Kabul province had the highest number of casualties in the first three months of 2017 thanks to multiple attacks in the capital.
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On May 31 a devastating truck bomb tore through Kabul's diplomatic zone at rush hour, killing more than 150 people and blowing out windows hundreds of metres away, adding to the already high toll in the city this year.
Six civilians seeking work in Farah, capital of western Farah province, were killed yesterday when their pickup truck hit a roadside bomb, provincial governor Nasir Mehri told AFP today. Authorities blamed the Taliban insurgency.