Children often run temperatures with no other symptoms. They need to be cooled down and then will feel much better. So do remove their clothes down to vest and pants and keep the room temperature down.
The arms and legs are the body's radiators, so don't prevent them getting rid of excess heat by covering them up.
Use Calpol/Disprol and if necessary sponge them with lukewarm - not cold - water. If there is no improvement and the child seems ill, contact the Doctor for further advice.