A temperature between 97 and 100.3 degrees Fahrenheit is considered normal for babies. Babies have a fever when they have a rectal temperature over 100, according to Mayo Clinic.
Fevers in babies are treated by bathing the baby in warm water, dressing the baby in light clothing and keeping the baby hydrated. Tylenol or ibuprofen is given with a doctor's approval, reports Mayo Clinic.
Babies under 3 months old need immediate medical care if they present with a fever. Other babies need to visit a doctor if they have a rash, problems breathing, become lethargic or have a seizure, according to Mayo Clinic.