The children had gathered around the Nato convoy for fun when the bomber struck, said Abdul Rahim Ayubi, a lawmaker from Kandahar.
Eight Romanian Nato soldiers were wounded.The Islamic State group claimed the Kabul bombings in a statement posted online, saying it targeted the Afghan intelligence headquarters.
In a separate attack in the eastern Khost province, a 29-year-old reporter for the BBC's Afghan service was shot dead by unknown gunmen.
The BBC confirmed the death of Ahmad Shah, saying he had worked for its Afghan service for more than a year. BBC World Service Director Jamie Angus called it a "devastating loss."
Stanekzai said the first suicide bomber was on a motorbike, while the second targeted those scrambling to the scene to aid victims. He said the second attacker was on foot in a crowd of reporters, pretending to be a member of the press, when he set off his payload.
AFP said the news agency's chief photographer in Kabul, Shah Marai, was among those killed.
Hundreds of people attended his funeral this morning.
Media watchdog Reporters Without Borders (RSF) said it was the deadliest attack targeting reporters since the US-led invasion that overthrew the Taliban in 2001.
The Paris-based group named the nine journalists killed, who worked for media organisations from multiple countries, and said another six reporters were wounded.
RSF said 36 media workers have been killed in Afghanistan in attacks by Isis or the Taliban since 2016.
Survivors of the attacks in Kabul recounted scenes of mayhem.
"When the explosion happened, everywhere was covered with dust and fire, it was such a horrific scene," said Jawed Ghulam Sakhi, a 28-year-old taxi driver. "I saw journalists covered with blood."
- AP