At least 15 street kids have been killed in the past week in the Democratic Republic of Congo diamond capital, Mbuji Mayi.
Some were burnt alive, beaten or stoned to death, officials say.
Some reports say that they were killed by local diamond miners, after the children stole some of their equipment.
Meanwhile, a report says that DR Congo is losing millions of dollars each month through the smuggling of cobalt and copper.
China had recorded 10,707 tonnes of cobalt concentrate being imported from DR Congo in March 2004, but the Congolese central bank had recorded cobalt production of just 783 tonnes, said campaign group Global Witness.
"This discrepancy raises serious questions about where mining revenues are going and how trade and production is being recorded," the group said.
Diamonds are another of DR Congo's major mineral exports and Mbuji Mayi is the centre of the diamond trade.
It is thought there are some 8,000 streets kids living in the city - second only to the capital, Kinshasa.
"It seems that some of the street kids had seized some of the equipment miners use so they [the miners] set up a defence force and things got out of hand," Social Affairs Minister Ingele Ifoto told Reuters news agency.
Some local reports say that up to 30 street kids have been killed over the past week.
"The authorities need to maintain calm and public order and ensure that the children are being protected," said Unicef child protection officer Trish Hiddleston.
Unicef staff have recovered the bodies of six children, aged around 15.