A high temperature for a baby depends on the baby's age, states Mayo Clinic. Infants who are up to 3 months old have a high temperature at 100.4 degrees Fahrenheit or higher. For babies between 3 and 24 months, a temperature of 102 degrees Fahrenheit or above is considered high.
For infants between 3 and 6 months old, it is important for caretakers to note irritability and lethargy in addition to temperature. Babies in this age range are considered to have a high temperature when discomfort and lethargy are paired with an elevated temperature up to 102 degrees Fahrenheit, explains Mayo Clinic.
Caretakers should seek medical attention for any baby up to 24 months who demonstrates vomiting, listlessness and diarrhea in addition to a high temperature. If the caretaker is unsure whether the baby is ill, he should always contact the baby's physician, advises Mayo Clinic.