Crowley was fussing. Well, Crowley wouldn't call it fussing, he would call it a sensible and reasonable putting forth of his argument for why this was A : not necessary, and B: not needed. ( It might have helped if someone had told Crowley that theses were the same two points)
Aziraphale would call it unnecessarily detaining breakfast.
Crowley had so far put forth the sentiment that he didn't need diapers. Which neither of them believed. Then that Crowley could change his own diapers, which Aziraphale wouldn't allow. Then Crowley had suggested that he just miracle his bladder away all together. Which Aziraphale really wouldn't allow. "All of your organs are in your corporation for a reason Crowley. Except maybe the appendix, I'm not entirely certain what that does."
Crowley helpfully offered "Randomly explode and kill you?"
Now it was quite a bit later than Aziraphale had planned on having breakfast, and Aziraphale was getting hungry and maybe his angelic composure was slipping just the smallest bit and he was getting a teeny bit cross. So he gave Crowley a firm but gentle smack to the backside and told him "That's enough, don't be naughty. Get onto the bed, so I can change you."
Aziraphale wasn't prepared for the look of utter betrayal that graced Crowley's face, as all fight seemed to instantly drain from the thin demon as he shuffled with resignation over to the bed and laid himself out on the changing mat. Than covered his face with his hands and stayed that way for the rest of the diaper change.
Aziraphale couldn't shake the feeling that he had done something wrong. Crowley had always been rather sensitive under that thin varnish of cool bravado and swaggering hips.(though Aziraphale had always suspected that the swagger might be because Crowley had a few more vertebrae than most people) In Crowley's current state he was even more sensitive than usual. Aziraphale wasnt sure if it was the smack to his bottom, or the bit of crossness that Aziraphale had let seep into his tone that had set Crowley off. Whatever it was he resolved to never do it again. He didn't like the quiet and reticent demon it left him with.
He dressed the demon in a plain black onesie he miracled up, and slipped a pair of grey shorts, with three little silver buttons on the front, up and over Crowley's diaper. He placed soft red socks on his feet, (no need to bother with shoes, Aziraphale highly doubted they would be leaving the bookshop) and placed a red paci in Crowley's mouth.
Crowley let Aziraphale carry him and spoon feed him eggs and toast with jam. He didn't fuss when Aziraphale tipped a sippy cup of cold milk up to his lips. Or when Aziraphale wiped off his slightly stick face with a wet napkin.
Aziraphale was getting a bit disquieted at this point. He had to din something to make things better, so he asked Crowley what he would like to do today. Crowley just mumbled back that it didn't matter. Aziraphale insisted and Crowley hesitantly asked something about a Prince, which confused Aziraphale.
"Could you say that just a bit louder darling?"
"Could we finish reading the Little Prince?" Crowley asked in a slightly more audible mumble.
Aziraphale was delighted. "Oh you remember that!"
Crowley nodded. "Wanna hear the end."
"Of course dear boy! Of course!"
Aziraphale bustled about, tucking Crowley onto his lap with the angel and devil bears and giving him a sippy cup of juice to suck on. He found where they had left off and began to read.