Based on the description of the dot plot, if the distribution of siblings is largely centered around a specific value with a few extreme values on one side, it is likely skewed. For example, if most of the dots are clustered at lower numbers with a few higher numbers, the distribution is right-skewed. In this case, the median would be a more appropriate measure of center because it is less affected by outliers than the mean.
To find the mean, add up all the values of siblings represented by the dots and divide by the total number of values. For instance, if the data points were 0, 1, 1, 2, 2, 3, 3, 4, 5, the mean would be (0 + 1 + 1 + 2 + 2 + 3 + 3 + 4 + 5)/9 = 2.33, while the median, which would be the middle value when arranged in order, would be 2. Therefore, the best measure of center for the number of siblings in this case would be the median, particularly if the data is skewed.
(Note: The specific calculations of mean and median depend on the actual data points in the dot plot, so replace the example figures with the actual numbers from your plot to get accurate results.)