Fever is a reaction of the body to different pyrogens released during any Infection. Usually temp more than 99 F is taken as fever . Mostly in children fever is because of viral infections like flu or RSV where the fever is there for 4-5 days but may persist even upto 2 weeks . Initially antipyretic like paracetamol is given in a dose of 15 mg / kg/ dose. Can be repeated after 4-6 hrs if needed . Lukewarm sponge bath can be given as home remedy to decrease fever. Adequate fluid intake is also beneficial. Urine output monitoring is necessary to avoid dehydration .

Use medicine if temperature is more than 100.4

Yes, you can use if the temperature is above 100 degrees Fahrenheit because he might go dull or there might be fatigue due to fever.