The death toll from the day's fighting included at least three children besides the bomber, and dozens of civilians were wounded in firefights as violence appeared to escalate after the Taliban announced a spring offensive.
The boy - thought to be one of the country's youngest-ever suicide attackers - detonated an explosive vest in a marketplace in Paktika province near the Pakistan border, provincial spokesman Mukhlis Afghan said.
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"The head of Shkin district council, Shair Nawaz, a woman and two other men were killed and 12 others were wounded," he said in a statement.
The Afghan interior ministry had earlier put the death toll at three, with 11 wounded.
It was unclear how authorities established the age of the bomber, with the bodies of suicide attackers often difficult to identify.
Taliban spokesman Zabihullah Mujahid claimed responsibility for the bombing on behalf of the group, which he said was behind all but one of Sunday's attacks. He told AFP they were part of the Islamists' fresh offensive.
In Logar province militants ambushed a convoy of NATO troops, starting a firefight in Baraki Barak district in which three children were killed by Taliban fire, district governor Mohammad
Rahim Amin told AFP.
In neighbouring Ghazni province, insurgents ambushed a police vehicle and sparked an exchange of fire, said deputy provincial police chief Mohammad Hussain.
"Two policemen and two civilians including a woman were killed," Hussain told AFP.
Another 13 civilians were wounded when a bomb attached to a bicycle parked in front of Ghazni police headquarters exploded on Sunday, he added.
The Taliban have announced their spring offensive would start on Sunday, with spring and summer the traditional fighting season in the country.
