Aaaaaand this guy's deviantart page is almost all of this combined
http://undiesboy.deviantart.com/
I read this guy's post about why he does what he does, he's got some preeeetty loveist opinions. Apparently the whole reason it's always boys is because
"This difference between the boys and the girls in these families creates a dynamic in which boys are thought of as being unclean, lazy and immature, whereas girls are more mature, modest, demure and self-disciplined, greatly concerned about their hygiene and how they present themselves, especially taking pride in the clothes that they wear. Some of the girls may be more open towards letting their brothers see them in their underwear as a gesture to show how they can keep their bodies clean and their butts thoroughly wiped.
The boys' diapers are not merely an incidental element in the eyes of their sisters, but are, in fact, a central focus of attention. The girls indulgently revel in not having to wear diapers themselves and immensely enjoy looking at their diapered brothers and pointing out the various attributes of their diapers, mostly the fact that they are so thick and high-rising. The pure plain whiteness of their brothers' diapers contrasts sharply with the skin tone of their bare, skinny legs, and the size of their big diapers dwarf their lanky bodies. These girls call attention to their brothers not ever being able to wear pants because of how thick their diapers are, thereby forcing them to wear their diapers in full view at all times. They point out the way their diaper usage makes them smell bad and how glad they are that the diapers are as thick and as high as they are".
I do kinda feel bad though, because apparently when he was a kid his sisters were like that about him wearing diapers because of accidents "My sisters took great pride in being girls, telling me that girls don't poop themselves and don't wear diapers, which is why they get to wear pants and I don't. These impressions sank in very deeply and remained with me throughout my remaining childhood."
That aside, most of his backstory is actually pretty hot.
Poll