My Son has a pale red skin rash on his back arms and legs. Parts of it are round (back arms lower legs) but it is all over his buttocks help?

? Viral rash. Many viruses can cause the kind of rash you are describing. Also key to know if there are other symptoms such as red eyes, runny nose or fever. Your son's age also can narrow down the possible cause. Needs follow up with your doctor as soon as possible.