It is rare for children to become seriously ill with no warning. Based on your child's symptoms, you should usually contact your child's pediatrician for advice. Timely treatment of symptoms can prevent an illness from getting worse or turning into an emergency.
A true emergency is when you believe a severe injury or illness is threatening your child's life or may cause permanent harm. In these cases, a child needs emergency medical treatment immediately. Discuss with your child's pediatrician in advance what you should do in case of a true emergency.
The use of vaccines has led to major improvements in child health over a relatively short period. Many of the infectious illnesses you or your parents had as children, from chickenpox to polio to measles, no longer affect most children today.