UNICEF official Geoff Keele told a press conference in Baghdad that the casualties were the result of handling arms, ammunition and cluster bombs dumped at several hundred sites around Iraq.
Hundreds of surface-to-air missiles abandoned by the now-disbanded Iraqi army, many of them damaged and unstable, also pose a serious threat, he said.
In Haditha, northwest of Baghdad, around 30 children were killed as they searched through an arms depot to salvage metal for sale, an activity which has become commonplace in Iraq since the war, Keele said.
He said 133 children were killed or wounded in Kirkuk in the last two weeks of April, while an average of 20 such accidents a day are being reported from Mosul, another northern city.
In southern Iraq, children are involved in about one in five of accidents involving explosives and arms, said Keele.
He pointed out that the Baghdad region alone had around 100 sites for the manufacture of surface-to-air missiles out of a total of 1,000 sites spread out across Iraq.
"Nothing has been done" to cope with the danger, said Keele, urging the US-British coalition to take prompt action and to send in specialised teams. It was their obligation as an occupying force to provide for civilians' safety, he stressed.