Fever My older son is running temperature since yesterday what could be the cause
Other causes of fever(High temperature) in babies include Reaction to a vaccination, Poor sleeping, Poor eating, Becoming overheated from being dressed too warmly or spending too much time outside on a hot day.

If your baby has been experienced this for more than 2 days. It will only be right to see a doctor asap. Please, don't self medicate
If your baby has a fever, in most instances it means they have probably picked up a cold or other viral infection. Although they are less common in infants, pneumonia, urinary tract infections, ear infections, or a more serious infection such as a blood bacterial infection or meningitis may be causing a fever.