Timely immunizations are very important in a young child's life, but too many parents fail to heed the advice of physicians to have their children vaccinated early.

Sometimes, because of inadequate health insurance or simple procrastination, it is not until children are enrolled in day care or are even of school age that parents ensure that their kids' vaccination records meet minimum standards.

With that in mind, Mayor Kurt L. Schmoke has named this Saturday Baltimore Child Immunization Day, and the Junior League is sponsoring free immunizations at the Shepherd's Clinic, 1927 St. Paul St., in an effort to get families thinking in terms of preventive health care.

"There's a general push in medicine these days to prevent disease and illness rather than to treat it," says Dr. James Brayton, chief of the Department of Pediatrics at Franklin Square Hospital. For children, that means vaccinations against serious illnesses beginning in infancy.

"We essentially try to immunize for five different diseases in the first year of life," says Dr. Brayton. They are polio, diphtheria, pertussis, tetanus and HIB (a bacterial infection).

While polio is rare in this generation and diphtheria and tetanus are pretty much confined to developing countries, "whooping cough, or pertussis, can be very serious in the first two years of life," he says. "It can be fatal."

One of the risks in neglecting the HIB shot, Dr. Brayton says, is bacterial meningitis, "which can cause severe retardation and can even be fatal" in very young children.

He says the standard procedure for infants today is to receive an oral polio vaccine, and DPT and HIB shots at 2 months of age and again at 4 and 6 months. A child is usually immunized against measles, mumps and rubella at his 15-month visit to the pediatrician.

At 18 months, he says, a doctor will generally repeat the earlier series with booster shots.

The vaccinations Saturday include all of the above mentioned ones, for both infants and children. Hours are 10 a.m. to 2 p.m.