My 20 month old son experienced a high fever of 102-103 for 24 hours, then fever completely broke followed by a pink dots rash all body. wet cough?

Roseola: You are describing what is most likely Roseola. Roseola is a viral infection that presents first with several day's fever followed by breaking out in a rash all over the body. There is nothing special to do for the rash. It will resolve on its own. Follow up with doctor if cough becomes more frequent.

Evaluation: You should take him to his doctor to be evaluated to find the cause so be treated, those symptom are possibility of viral infection.