The girls were seen moments before the two attacks on a market in Maiduguri, northeastern Nigeria, on Sunday.
Abdulkarim Jabo, a militia member in Maiduguri, said he believed the girls were only seven or eight, adding: “They got out of a rickshaw and walked right in front of me without showing the slightest sign of emotion”.
He said: “I tried to speak with one of them, in Hausa and in English, but she didn’t answer.
“I thought they were looking for their mother.
“She headed toward the poultry sellers, then detonated her explosives belt.”
The second explosion came slightly later as onlookers rushed to help the victims of the first blast.
Bello Dambatta, of the local emergency management agency, said 17 people had been treated after the explosions, with “different degrees of injuries”.
He added: “The mutilated bodies of two suicide bombers were also evacuated.”
Among the injured were soldiers guarding a nearby electric power installation.
The attacks have not yet been claimed – but the jihadist group Boko Haram has a history of using women or children for such assaults, especially in Borno state, of which Maiduguri is the capital.
Boko Haram have been fighting Nigeria’s government since 2009 to impose hardline Islamic rule over the country’s mainly Muslim north.
During those seven years, at least 20,000 people have been killed, more than 2.5 million have had to flee their homes and thousands of women and girls have been abducted by the group.
The females can be used as sex slaves or human bombs, while boys are also abducted and forced to fight.
Last year, Nigerian president Muhammadu Buhari said the Islamic uprising had been “technically defeated”.
However, the Nigerian army is still struggling against the suicide attacks, looting and indiscriminate killing.
On Friday, Mr Buhari said Nigeria was working at “slamming the final nail in the coffin of Boko Haram”.
But that same day, at least 45 people were killed and dozens injured in another double suicide bombing carried out by two women at a market in Madagali, about 95 miles from Maiduguri.