Some reports said the children themselves, known as "chegues," killed a policeman.
The trouble started after a young boy was caught stealing vegetables from Kinshasa's central market, city council spokesman Fabrice Wazenge said.
"Another policeman shot a bullet into the running boy," said one witness. "Then a mob of enraged chegues swooped on the agent who had opened fire, beating him to death."
The children attacked a small police station and sparking a round of looting at a nearby market.
Police intervened, firing tear gas to disperse the children from the area. It took police half an hour to restore order as traders panicked, abandoning their stalls to looters.
Information Minister Kikaya Bin Karubi said the children wounded one policeman in the mayhem.
"At least 78 children have been arrested," said Amigo Gonde, of the Kinshasa-based African Association for the Defense of Human Rights.
It was not immediately clear whether any of the children were hurt.
About 15,000 unaccompanied children live on the streets of the impoverished Central African capital, according to the U.N. children's agency.
The chegues, from a few years old to their late teens, are victims of decades of decline and conflict in the Democratic Republic of Congo, Africa's third biggest country.
DRC, formerly Zaire, was wracked by civil war in 1997 when Laurent Kabila ousted dictator Mobutu Sese Seko.
War broke out again in 1998, when Kablia's former allies Uganda and Rwanda launched efforts to overthrow him, objecting to his leadership style and his reluctance to crack down on Hutu groups based in eastern Congo.
Now, at least six nations Uganda, Rwanda, Burundi, Angola, Namibia and Zimbabwe are involved in the war. A peace accord was signed in 1999 but there is still not full compliance.
Kabila was assassinated in January and replaced by his son, Joseph Kabila.
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