Southwestern Connecticut parents are concerned after a major distributor of a children?s flu vaccine announced it is behind on its October shipment.Health officals at Willows Pediatrics in Westport are telling parents not to worry after word from Flu Zone of the three-week delay. They say they received a partial shipment earlier in the month that will last them through the next allotted delivery period. The vaccine company says deliveries will return to normal in November and December.Those most susceptible are children between the ages of 6 months and 5 years. Children undergoing chemotherapy or suffering from asthma are also prone to sickness. Doctors say although the delay is no cause for alarm, they urge parents to take proactive steps to keep their children healthy. They say these steps can be as easy as washing their children?s hands, blowing their noses and keeping them home from school when they have a fever.