According to a Center for Disease Control and Prevention (CDC) study, one in four toddlers are improperly vaccinated. Missed doses or improperly timed doses make up for the majority of immunization errors in children who are 19-35 months old.

Though immunization rates in the US remain good overall -- and the rates of children who are immunized by kindergarten age are higher than ever -- the CDC recommends children being vaccinated at the proper, recommended times. So, in addition to relying on your pediatrician's recommendations, it's important for parents to do their own homework.

For more information, see the CDC's information on vaccines.