Sorry your little man is sick

Im not much help, but just wanted to say, dont let him get too cold either. If he gets shivery it will make him warmer as the body shivers to produce enrgy and therefore heat when you are cold.
A Luke warm face washer or bath would be enough, it shouldnt be cold.
Also a temperature helps to fight whatever bug hes got so only treat it if its making him uncomfortable or is over a certain point -38.5 I think (you might want to check that, I cant remember).

His body will know what it needs and tell him to rest if he needs to so if hes happy to play Id just leave him.

And lots of fluids, if he'll take it, to help flush it out of his system.

HTH.