My 4 year old has high sudden fever , (38-39c ) , it goes down after taking calpol but comes back again in 6 hours.she has only very slight runny nose?

Common issue: Kids in this age group are expected to get 4-7 viral illnesses/yr and many will present this way. Most will self heal over a few days to a week. As long as the kid takes fluids well enough to pee every 8 hrs or better, feed enough to be active & plays some it can be monitored at home. Fever meds may or may not take a degree or two off the top for a few hours. It can be used as needed for comfort.