The figures were a slight improvement from 2010 when 25.957 million children faced the same plight, the agency said.
Romania and Bulgaria were the worst off in the 28-nation bloc with 46.8 percent and 43.7 percent of their children at risk, while Scandinavian countries fared best.
Overall Eurostat said 25.264 million children under 18 years old, or 26.9 percent of the population in that age group, were in the at risk zone.
These children live in households with at least one of the following conditions: social benefits fail to meet their needs, insufficient material standards and their parents have little or no work.
The figures were a slight improvement from 2010 when 25.957 million children, or 27.5 percent of the population faced the same plight, the agency said.
Romania and Bulgaria were followed by debt-hit Greece (37.8 percent), Hungary (36.1 percent), Spain (34.4 percent), Italy (33.5 percent), Lithuania (32.7 percent), Latvia (31.3 percent), and Britain (30.3 percent).
At the top of the scale, children in northern countries like Sweden (14 percent), Finland (14.9 percent) and Denmark (15.7 percent) fared best.
The agency said low levels of parental education significantly increase the risk of poverty or social exclusion.