This is equally applicable to adults. Adults are fit from Mon-Fri and fell ill on Sunday because of disturbance in routine. By our experience we have felt that babies having a routine with the creche are perfectly health till Saturday. When babies come on Monday after a break of Sunday some of them catch flu/fever or other digestive of respiratory disorders. The hidden reason we have found is due to change in diet pattern of baby on Sunday, Travel stress and bad weather. On holidays parents go for outing; take dinner at restaurant/hotel/mall at odd hours..this probably disturbs biological clock and health of the babies..