Call your doctor if your toddler has fever with a temperature of higher than 102.2F or 39C and it has continued on for over 72 hours. Since it has only been 12 hours, take into account your child's disposition as well. It's probably not serious if your child is still eating, drinking, playing and seems alert. Alert your doctor and go to the ER if your kid won't stop crying, is sluggish and has trouble waking up, is limp or won't budge, is extremely irritable or fussy, or has blue lips, tongue or nails.