What Could Cause Itchy Rashes On The Legs?

My 3 year old has been having some bumpy rashes on his legs. He keeps scratching it so i know it must be itchy and bothers him. Then around his thighs especially near his buttocks he has this circle redish rash. His legs cleared up i noticed when I stayed at my parents who have tight carpets and mostly wood floors. Our place on the other hand have carpets in every room and are very loose and I'm afraid causes the rash. I don't know what to do because it's going everywhere on his legs. It's beginning to grow some small bumpy rashes almost an inch away from eachother. Pls help!