In Japan's stricken nuclear plant area, around 45 percent of children were found to have traces of radioactive elements in their thyroid glands, says an official.
The official said that the iodine concentrations -- found in tests that the government carried out about five months ago in Fukushima prefecture -- were not considered alarming in terms of their health impact.
"The government's official position is that none of the children showed radiation levels that would be problematic," he told AFP.
The government's nuclear accident taskforce tested 1,149 children aged up to 15 about two weeks after the March 11 earthquake and tsunami triggered meltdowns, blasts and fires at the Fukushima plant.
Radioactive iodine tends to gather in the thyroid glands of minors in particular, increasing the risk of developing cancer later in life.
Of the valid test results collected for 1,080 children, 482 or 44.6 percent were confirmed to have some level of radioactive contamination in their thyroid glands, the government official told AFP.
The official, who spoke on condition of anonymity, said none of the children suffered contamination beyond the equivalent of 0.2 microsieverts (mSv) per hour, the standard set by Japan's Nuclear Safety Commission.
"Only one child showed a contamination level of 0.1 mSv per hour, the highest of the group," the official said without giving the child's sex or age.
The commission recommends that children, especially young ones, whose thyroid gland is contaminated beyond the 0.2 mSv limit undergo an in-depth physical checkup, citing international standards.
The commission is considering tightening its safety standard to 0.1 mSv.
The children tested came from three municipalities -- Iwaki city, Kawamata town and Iitate village -- where especially high levels of radiation had been estimated after the accident, the official said.
The Fukushima government plans to conduct life-time medical checks for the estimated 360,000 people aged 18 or younger who were in the prefecture at the time of the nuclear accident.
The taskforce medical team began sending test results to the families of the children last week and gave a briefing on Wednesday to a group of parents and guardians in Iwaki city.
Some participants complained that the team took months to inform them of the detailed results despite the gravity of the nuclear accident, the world's worst since Chernobyl 25 years ago, the Asahi Shimbun daily reported.
The government official said the taskforce did not consider informing the families of the details results as a priority since no child had shown contamination levels beyond the safety limit.