A temperature of 102 F to 104 F is usually okay for a child or adult since the fever will be helping to fight off viruses.
If your body temperature or a child's body temperature stays at 102 F for too long or goes above 104 F you should then go to the emergency room and for an infant you should take the infant to the emergency room if the infants temperature stays above 102 F for too long and doesn't go down within a few hours.