4 year old son had rash on groin area, 2wks later 5 yr old has rash same area and spots all over body, I had under my breasts what could this be?

Possibilities. It sounds like this could be ringworm- usually this happens in perineum or areas where skin rubs against skin, and can be more diffuse. Another thought is impetigo, another rash that can spread among people in close contact. Best for your md to see.