Final answer:
A child's weight at the 50th percentile on a growth chart signifies that their weight is greater than or equal to that of half the children of the same gender and age. This measurement indicates an average weight status among peers.
Step-by-step explanation:
When a child's weight is plotted at the 50th percentile on the growth chart, it means that the child's weight is greater than or equal to the weight of 50 percent of the children of the same gender and age. Percentiles in a growth chart are used to compare a child's growth to a reference population. The 50th percentile is the median value, and being at this percentile would indicate that the child's weight is considered average among peers of the same age and sex.
For example, if a girl is at the 50th percentile for weight on a growth chart specified for girls her age, she weighs more than or equal to half of the girls in that reference group. The growth charts typically do not take ethnicity into account, so the comparison is mainly with respect to age and gender.