Based on the comic.
When Bart entered Maggie's room, he would always find Maggie whimpering and fidgeting in her crib. He also believes that she was whimpering was because her pacifier was not in her mouth. "Well, I don't lose anything for trying. No need to cry, sweet Maggie. Your big brother is here for you. First thing I'm gonna do is rub your cute tummy and see if you'll calm down immediately. Your big sister loves it when I rub her tummy. Again, I will try this to see if this will calm you down." Bart then went down and slowly rubbed his sister's tummy, which led to Maggie starting to calm down immediately. "Yep, she's starting to calm down. Here's your signature pacifier, baby sister. Okay, let's try something else." The young man slowly removed his sister's pajamas, leaving her in nothing except for her diaper. Because she knew what her big brother was doing for her, Maggie could think of only one thing: he was going to take her to the changing table. "It looks like you're pointing to that changing table over there. You're right, because I'm about to change your diaper, sweet Maggie, so let's take you to that changing table over there." he said quietly. "Big brother." Maggie said dreamily.
So, Bart picked up his baby sister from her crib as the two young siblings headed for the changing table, where he laid Maggie down. There, he would slowly undo the tapes on her diaper, removing it and throwing it in the diaper bin, meaning that Maggie was now naked. "Mmm..." Maggie said quietly. "Oh, baby. It's gonna be alright, my sweet baby sister. You're still clean. But it's been nearly two hours, so I'm gonna change your diaper anyway." So, Bart grabbed a baby wipe and used it to slowly wipe Maggie's private area clean. In response, Maggie made soft sucking sounds with her pacifier and did not move an inch. "Mmm..." Maggie said again, embracing the moment. Then, Bart got the baby powder and applied it to Maggie's genitals. After 5 minutes of staying still, because of her genitals still being made contact with his bare hands, Maggie decided to slowly move her legs. "Oh, my sweet Maggie Simpson. You like what I'm doing with your pee-pee, don't you? Mmm... (2x)" After that, Bart would apply a little more baby powder to his sister's bottom. Finally, he got a new diaper and wrapped Maggie's bottom in it. "All clean, my sweet baby sister." he said sweetly, giving his baby sister a kiss on her right cheek as the two siblings went back to Maggie's crib. "Sweet dreams, younger sister."
Then, Lisa, in her sleeping dress, saw her brother soothing Maggie by tucking her in bed. "Bart, is that you? Yeah, sis. Oh, okay then. Why does Maggie look like that, and why is there a stain on your shirt? Oh, I just changed her diaper." Hearing this, Lisa's face went from confused to surprised. "Really? All by yourself? Yep, without any hardships. Oh, I'm so proud of you, big brother." she said happily, giving her big brother a hug. "But, here's something special that happened. Okay. That's why your shirt has that stain. When I applied baby powder on her genitals and made contact with them, she slowly squirmed by moving her legs, so I had to get my fingers out of there quick. That's strange, because babies aren't sexual like that. But, when she felt your fingers making contact with her genitals, I guess she liked it a lot. She loved your somewhat sexual feelings towards her, although you were trying to keep her clean and dry. She did the same thing when I changed her. What else happened? She enjoyed the moment by relaxing, softly sucking on her pacifier, and didn't move an inch with her eyes closed. Then I guess both of us made contact with her genitals a lot because that's what happens when changing diapers. Contact with the baby's genitals is made a lot. Plus, it's been two hours, because I remember Mom told me she changed Maggie prior to her and Dad leaving the house. Now, let's quietly exit this nursery and go back to your room, big brother." Bart and Lisa exited the nursery and went to his room, where they would spend some quality sibling time with each other before going to sleep.
In Maggie's head (since she can't talk on the show):
Yeah, big brother. Calm your sweet baby sister down immediately by slowly rubbing my tummy. Thank you. You're probably wanting to change my diaper for me. Well, I would like it because it's been almost two hours, so let's go to the changing table. First, get me out of my pajamas, since I'm usually naked when getting a diaper change. Slowly undo the tapes on my diaper, remove it from my behind, and throw it in the diaper bin. Now I'm naked like when I was welcomed to the world. Use a baby wipe and wipe my pee-pee clean. Oh, yeah. That feels good. The wipe may be cold, but it feels nice. Then, sprinkle a little bit of that baby powder on my pee-pee to keep it dry. That tickles. Sprinkle a little more baby powder on my pee-pee, and then get a fresh diaper and wrap my bottom in it, and you're done. Goodnight, big brother. I love you.
