State Health Department workers plan to visit every house in the Kern County farming community of McFarland in the next several weeks as part of a program to evaluate the health of all children up to the age of 12 in the town of 6,500. Residents with preteen children will be encouraged to make appointments at the town’s new health clinic. The screening is being done because of the unusually high childhood cancer rate in McFarland. State and Kern County health officials have not been able to determine the cause of the cancer cluster. At least 15 McFarland children have been diagnosed as having cancer in the last 15 years.