My little son age 4yrs when sweating smells really terrible and otherwise also smells bad after few hours of his bath.?

Is it his sweat ?: One of the most common reasons a kid smells bad can be foreign material stuck in their nose. They smell horrible until the material is removed. If your 4yo kid's sweat really smells it could be a sign of a metabolic problem & you need it checked out. I've had some kids smell a bit odd if they consume a variety of products like aloe juice or from lotions applied to their skin.