Our daugter had a mild case and her doctor prescribed Aldera. It only made it worse.
We were referred to a pediatric dermatologist but couldn't get in for a couple of months. We decided to try ZymaDerm while we were waiting, and we were very pleased with the results (just not the smell). It stopped spreading and went away before we ever made it to the dermatologist.
I would check with your pediatrician, but our doctor said it was still ok for our daughter to swim. She just shouldn't share towels, clothes, etc.
I never tried it, but my sister-in-law swears that either clear finger nail glue or nail polish does the trick. I can't remember which one.