The One About the Rain Boots

Gavin had seen these rain boots at Wal-Mart awhile back, but they didn't have his size.  On Friday, I saw Target had a similar pair.  He was SO EXCITED!  He has had them on constantly this weekend, even asking me if he could wear them in the bathtub.  He thought I was an idiot for saying no.  "But Mommy, they're rain boots.  They can get wet."  How do you explain that one to a 4-year old?