When should I bring my 15-18 month old child to the doctors if I suspect that my child is sick?

Four signs. If your baby 1) is fretful or irritable for more than 24 hours, 2) has fever that is lasting more than 48 hours, 3) has temperature higher than 103.5 degrees rectally, or 4) screams and cannot be calmed down in 3 hours.