When germs enter our body, the immune system recognizes them as foreign substances (antigens agents); therefore, the system itself is responsible for putting the production of the required amount of antibodies in place to combat these antigens. Based on this process, the vaccines contain weakened or killed antigens that stimulate the immune system to produce antibodies. Specifically, vaccines for children simply to help eradicate certain infectious diseases, some of them fatal form. Although side effects may occur after administration, the benefits of vaccination far outweigh the possible occurrence of such effects, which are usually mild. Compulsory vaccination schedules exist in almost all countries, and in Spain varies by the Autonomous Communities. Therefore, it is important that parents inform themselves under the guidance of doctor of vaccines that correspond to their children and at what stages or moments of his life.