Children should be vaccinated according to a schedule recommended by health authorities such as the Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO). This schedule is designed to provide immunity at the optimal time when children are most vulnerable. For example, the first dose of the Hepatitis B vaccine is often given at birth, while others like the MMR vaccine (Measles, Mumps, Rubella) are given at 12-15 months of age.
