It can sometimes be hard to tell if someone is wearing a diaper.
Although you can sometimes tell if someone is wearing a diaper by looking for a diaper peeking above the persons pants, shorts etc when their shirt rides up.
Also if someone is wearing a diaper that is bulky then you may notice a bulge in the front of the pants and even in the back of the pants.
When I'm wearing sweat pants and I wear a thick bulky diaper I can see the outline of the diaper bulge in the back of my sweat pants and in the front of my sweat pants.
With blue jeans I can see the back of the jeans are pushed outwards some.
I have seen older kids above age 3 wearing diapers in public.
A few days ago I was at Taco Bell and eating some Tacos and the kid in front of me at the booth stood up and I could see a Pampers Cruisers diaper sticking above his waistband of his blue jeans.
He looked to be around 7 years old and looked very normal.
I'm not sure if he was incontinent or just was not potty trained and wanted to wear diapers instead.
I also saw another kid the same day in Dollar Tree who looked to be around 6 years old and it was a boy and he was wearing a Luvs diaper.
I saw the waistband and part of the back of the Luvs diaper stick above his pants when he bent down to look pick up some toys from the shelf.