vintage boys pants...

My son is a very solid 3.5 year old. I'm told by the dr that I don't have to worry about his weight, but he's not a skinny minny. His shoulders are so wide, that if I buy a woven shirt, he needs a 7-8... (he's like his dad in that respect) His waist/hip (cause he wears his pants right about at his hip bones)measurement right now is almost exactly 22", which is an inch bigger than the measurement for this awesome pair of vintage boys pants...

plus, I'm not sure, when it says "size 4, waist 21" if that means the boys waist measurement, or the finished pant size...

granted there's elastic in the back, but I am planning on attempting my first resize to add an extra 2" to the width. I found this awesome looking explanation of how to do it here...

my gram gave me this old sheet, which maybe is the ugliest fabric I HAVE EVER SEEN (she didn't want to give it to me for precisely that reason, but it's free and totally fine for making boy pant muslins, right?

I guess my cat is color/pattern-blind, cause he thinks this is a great kitty bed...