Dudes have stores across the street from each other, with children's sections as big as a freakin' house, but they don't even have restrooms? WTF.
So unless you want to teach him about hanging one over the atrium balcony--and at this point, I wouldn't disapprove--don't let your kid-in-toilet-training set foot in an H&M.
As for diapers, I recommend changing them on the checkout counter.
Yeah, I experienced that. A worker directed me to a Burger King way down the block, I was pretty annoyed.
The same thing in san francisco -- two H&Ms within a stone's throw. The one in the mall doesn't have a bathroom that I could tell. But some of the clothes need improvement anyway, so ...
Just in Sanrio the other day in Times Square with my four year old. Sanrio!!!! And they don't have a bathroom available for use for kids.
Thats why I always carry a a couple portable changing pads and diapers in my diaper bag, and, never leave home without it!LOL