My sister, 5' 1" and maybe 100lbs., and her husband, 5' 5" and maybe 125lbs, have a seven-year-old daughter, my darling niece, who is quite small for her age, in the bottom percentile for her age in height and weight, actually. Looking for a possible cause beyond simple genetics, i.e., that both her parents are very small people, her pediatrician conducted...