A baby with Down syndrome has some distinct facial features which can include almond-shaped eyes (due to epicanthal folds); light-colored spots in their eyes (called Brushfield spots); a small, somewhat flat nose; a small mouth with a protruding tongue; and small ears. They also have round faces and somewhat flatter profiles.
None of these facial or physical features are abnormal by themselves, nor would they cause a baby with Down syndrome any medical problems. But if a doctor sees a number of these features together in one baby, they begin to suspect that the baby has Down syndrome. These facial and physical features are what cause people with Down syndrome to resemble one another, although they also resemble their own families.