How did my baby get ringworm?

My baby is 4 months old & we are home 24/7. I believe he has ringworm on his chest. (Where a necklace would lay) It’s a red circle.. I’m not sure how he could get something like that? I’ve never had that.. I give him a bath every other day and wash his blankets a couple times a week.. but his dad is a barber. He thinks that’s how our son got it cause he touches people .. I feel so gross & embarrassed 😱 He doesn’t have it though. Our son is seeing a doctor tomorrow, but I was curious on how you get that?

Update: we have 1 inside cat.