It's well documented that Ls are hard for Simon and, while Ss and Ws are fine alone, the combo really throws him. For documentation purposes, here are a few more words to add to his list:
Fweatshirt - Sweatshirt
Fwings - Swings
Wiberty - Liberty (our Jeep Liberty, specifically)
Wowwipop - Lollipop
I'm sure he'll love hearing about this when he gets older ...