Rash or bug bites?

I gave birth in December and just went back to work last Monday. My mom has been watching my baby at her home. Last Thursday I noticed little bumps on his legs and a few on his back. I was worried she didn’t know were they came from. Now today when I was getting him ready for his bath, there were MORE bumps. I really freaked out asking how the hell did he get bug bites. She don’t believe they are bites and is saying it’s from the detergent I use. What do you think?