According to the report, Economic and Living Conditions for Low-Income Groups, 15.6 percent of children in Oslo come from families classed as poor, more than double the 7.6 percent rate for the country as a whole.
The agency points the finger at the capital's high number of immigrants, who are over-represented in poverty statistics.
As many as 67 percent of Somali children and 41 percent of Pakistani children come from families classed as poor, the agency reports.
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The European Union defines a poor family as one where the income is below 60 percent of the median income for the country in which they live.