Final answer:
Children below the 30th percentile are considered to be below average as it indicates that 30 percent of the population falls below this point in a measurable characteristic.
Step-by-step explanation:
Children below the 30th percentile are considered below average. In statistical terms, percentiles rank the position of an individual by indicating the percentage of a distribution that is equal to or below a particular value. When describing children or any population in terms of a measurable characteristic, such as height, weight, or test scores, the 30th percentile means that 30 percent of children fall below this point, suggesting a lower than median performance or characteristic measure.