The Ohio State College of Medicine conducted a comprehensive study of incidents involving escalators and injuries to children. There were approximately 26000 escalator related injuries to children between 0 and 19 during the time period between 1990 and 2002. The study showed that about 40 % of the children were under the age of 5. The average age of the children was 6.5 years of age.
Proper design and maintenance are important to help avoid escalator related injuries. It is also vital that parents and caregivers closely supervise children while riding escalators. You can read more about the study at Escalator Related Injuries to Children in the United States.