Final answer:
The specific percentage of children living below the poverty line in the US in 2010 is not provided, but trends indicate a high poverty rate close to the peak of 15.9% seen in 2011. Official U.S Census Bureau data is required for an exact figure.
Step-by-step explanation:
The question focuses on the percentage of children living below the poverty line in the United States in 2010. However, the provided information does not give a specific figure for 2010, but it indicates that the poverty rate has fluctuated over time. Through historical trends, we know that the poverty rate declined through the 1960s, increased in the early 1980s and early 1990s, and then was slightly lower from the mid-1990s. In recent years before 2010, the poverty rates peaked at 15.9% in 2011, with the lowest rate in the preceding four decades being no less than 11% of the U.S. population.
Based on the trends, it is reasonable to infer that in 2010, the poverty rate, and thus the proportion of children in poverty, was relatively high, likely close to the peak of 15.9% seen in 2011. It is important to examine official U.S. Census Bureau reports for precise data on the poverty rate among children in 2010.