My son is 3 he started with fever and sore throat with small red dots then fever was gone and he had chicken pox like bumps that never had pus or scabbed over now all of that has gone away and he has runny nose and small cough I can't figure this out and my daughter has just started same symptoms please help

Time to get them both to the Doctor, there is no way to diagnose these things over the internet.
I hope they are better soon.

Yea go see a doctor there might be a reason for a weak immun system like that