Explosions on 22 March at the Malhazine national arms depot, about 10km from the city centre, showered more than 4,000 pieces of ordnance into 14 densely populated neighbourhoods, killing more than a 100 people, wounding more than 500, and destroying dozens of homes.
The three children - an 11-year-old and 13-year-old twins - lived in Magoanine, about a kilometre from the arms depot, one of the neighbourhoods worst hit during the March explosions. The children were lighting a fire above an unexploded weapon that had been buried in the ground, which set it off, according to Notícias, the state-run newspaper.
This week's accident occurred after Mozambique's embattled defence minister had declared the area free of live ammunition, after what many observers described as a sometimes haphazard recovery effort.
A not-so-thorough recovery?
"The effort we saw was quite impressive," said Gilles Delecourt, country director of Handicap International, a non-governmental organisation (NGO) that does demining work in Mozambique and helped locate ammunition debris in the weeks following the explosions.
The army's methodology, which consisted of bands of soldiers piling possibly volatile rockets into flatbed trucks, had not been by the book, Delencourt said, but added that "it was an emergency situation".
Some observers were surprised that the recovery produced no accidents, and said some weapons were likely to have been overlooked in the rushed process.
In recent months there have been other explosions involving ammunition debris in at least four other neighbourhoods, according to Zambeze, an independent weekly, although none of these resulted in injuries. Army recovery teams were once again at work after Tuesday's accident.
Dan Bridges, country director of the HALO Trust, a UK-based NGO that specialises in removing the debris of war, said a 100 percent recovery of weapons would be difficult "without incurring a massive population movement and searching every square centimetre of ground".
He said it was important that officials maintained open lines of communication with residents. "You can only find and deal with the items that are known about, so you need a strong reporting structure that people are aware of, and an emergency response to go and deal with it."
In the weeks after the March explosions there was a large publicity campaign encouraging residents to contact the army about weapons on their property, and warning people against handling the weapons themselves. However, some residents have complained that after the first few weeks their calls went unanswered.
The Malhazine disaster brought worldwide attention to the poor country's inability to secure or dispose of hundreds of tonnes of deteriorating armaments left over from Mozambique's 17-year civil war, which ended in 1992. The military has said it would either relocate the weapons to more isolated areas or destroy them in a safe manner by the end of this year.
Government officials blamed the March explosions on excessive heat. Prior to that accident, at least 18 people had been killed as a result of explosions at arms depots in Maputo and Beira, the country's second largest city, since 1985.
In December 2006 five people were killed in Beira by unexploded ordnance that that had been lying in fields since an explosion at the local depot in 2003.