For a good ten minutes, I was trying to work out how someone would use such a small box to change out of. "does it fold out into some silly cardboard variation of a Victorian privacy screen..." etc.. thoughts until I finally re-read it. 

Damn skim reading got me assuming again.

That's actually why the dad believes the baby is a late bloomer; It took him this long to get a concussion? He's practically a toddler now!