"I do not know much about babies besides the fact that they are quite small." Angewoman said "And you two are quite small." It occurred to the two girls that Angewoman was comparing her own size to theirs.
"You're wrong!" Mimi shouted "There's much more to being a baby than just being small!"

Kari did take a look and noticed that the Angewomon she was being carried by was larger than her Digimon's ultimate form. She have never seen much of her Digimon's forms or anyone else's outside their Digimons' digivolutions that she would never expect to be varieties out there. It seemed that there was no convincing the Angewomon that they weren't babies so Kari just flat out give up, not caring where she and Mimi were going to end up.

Angewoman took the two girls into a gigantic nursery. "I built this in case I ever had a baby of my own." she said "Looks like I can use it for you two." She set the two girls down on a table before starting to remove their clothes.
"What're you doing!" Mimi shouted.

Kari looked around and did see everything the nursery had. A crib, a changing table, a toy chest, a playpen, everything needed to take care of a baby. The shocking part was everything seemed to be best fitted for a person her and Mimi's size. Kari didn't protest much as she was laid onto the changing table, at least until she was being undressed. "Hey!!" Kari chirped, "What do you think you are doing? You can't just undress us!!"

"Well, you two can't just diaper yourselves can you?" Angewoman said.
"D-Diaper!" Mimi shouted out "You are not going to put us into any diapers! We! Aren't! Babies!"

Kari gulped at that world, her face all flustered and bright red. She never thought once that she and Mimi would be diapered. Although from the many times that Angewomon said that they were infants it would've been obvious from the start. "Uh....are you sure that we need diapers?" Kari asked, not trying to sound very mean towards the Digimon, taking in mind that she was an Ultimate leveled Digimon, "I mean I would settle for training pants at least but I don't really want to wear a diaper."

There was a reason Kari brought that up, of course. When she was littler she did have bouts of illnesses from time to time meaning she was too sick to get out of bed to do stuff like use the bathroom so she had to be diapered in bed all the time, which wasn't a fun experience for her so she clearly didn't want anything like that ever again.

"Infants like you aren't able to control their bowels or bladder yet." Angewoman said "I can't have you making puddles all over my house or messes in you clothes."
This infuriated Mimi. "I haven't once had an accident since I was three!" she screamed. "I'm not wearing a diaper! If you want to baby someone, pick an actual baby."

Kari did blush, not wanting to be diapered up or worst of all using them. Of course Angewomon didn't have to say that they needed to be used. That gave Kari a little idea. "Mimi," she whispered to her friend, "Angewomon thinks we can't control our bladders or bowels. Maybe if we play along and when we need to go to the bathroom we can just tell her. Hopefully she'll let us participate in potty training where we can prove that we aren't infants. Just calm down and don't get her upset."

"Fine." Mimi said "But I won't like it at all." She turned to Angewoman. "Alright, just diaper us quick."
With a small smile, Angemon fully removed the girls clothes and diapered them. "Now, doesn't that feel a bit better?" Mimi and Kari both blushed heavily.

Kari was blushing the whole time her swimsuit came off and a diaper was taped over her hips to replace it. Of course they were both wearing diapers and just that, nothing else. Just being in underwear next to someone would make her nervous. "Yes, I guess it does feel better," Kari said, playing along with Angewomon, "But I would feel a lot better if I had some clothes I can wear. I feel...a little chilly."