My Daughter Has Come Down With Flue Like Symptoms But

My daughter has come down with flue like symptoms but is running a fever , ie my thermometer say 39.4 but battery is running low , just by feeling her I can tell she is super hot, my son has had the same problem last week,and had a chance to take him for a couple of tests as well , dr just told him to take panadol and drink lots of water, now his body is cramping , and he is super cranky, but he is also 16 years old. Help please..?