An official with the National Centers for Disease Control is reminding parents about the importance of getting their children immunized by age two against a variety of diseases, some of which are rarely seen in the U-S anymore. Dr. Jane Seward says the list includes such once-common diseases as measles and whooping cough. She says children should have a total of about 14 vaccinations. She says despite the concerns of some parents, modern vaccines are quite safe, with reactions usually limited to such things as soreness and other minor health issues. Dr. Seward urges parents with questions about childhood vaccinations to consult their family physician.  She also says that families who may face a financial challenge getting their children vaccinated may want to look into the federal ''Vaccines for Children Program" for possible help with the cost of vaccinations. Dr. Seward made her comments in conjunction with National Infant Immunization Week.