Frustratingly, you are a man and cannot follow Kelsi into the bathroom. You have all this power over age, but you can't even break a simple social institution like bathrooms. You sigh in aggravation. Then you pause for a moment, "Wait..." you mutter to yourself.
A moment later, you are stood behind a large decorative shrub near a wall. Within this relatively weak privacy, you point the device to yourself and physically regress to the age of seven. You keep reality turned OFF, so that no one may be elected as your new caretaker, but set clothing to ON so that you may walk right out of the shrub fully clothed. After doing this, you pull the device in closer and aim it directly at your hair, as distinct from the rest of your body. Sure enough, as you had hoped, the device (so far as you can barely read it from this angle) is giving you a reading on your hair only, registering it as "of a seven-year-old. Two weeks since last cut." Perfect! You physically progress your hair up 10 months with no cuts, causing it to grow all the way down to your shoulder-blades. As you emerge from the shrub, you check yourself in your phone's selfie-mode and see it for yourself: with your young age making you largely gender ambiguous, your long hair makes you look like a girl.
You bolt over to the bathroom, and can already tell that Kelsi and Randal had gone into the big disabled stall on the far side of the room. By the sounds of things, Kelsi seemed to be getting Randal set up for something. You walk over to the stall directly next to theirs, making sure the lock is on tight and pulling down your pants and underwear to diffuse any suspicions of eavesdropping. First, you make a point to sit down on the toilet as a girl world, and then make sure your little boxers are tucked fully inside your pants so as to not be seen.
"Alright, honey, let's get you cleaned up." Kelsi says. You hear the ripping of tapes. You slyly bend down below the walls of the stall, and see that Randal has been hoisted up onto the changing station (a mercifully large one which holds adults as well as children), and is currently wearing an adult diaper. It would appear that you removed so much of Randal's knowledge, that he lost his understanding of potty-training as well. Kelsi tore the diaper off and picked it up. Not only had Randal been wearing a diaper, he had peed in it too! He had almost soaked it, in fact. You watched as Kelsi took out a package of baby wipes and began cleaning up his privates.
After the diaper change was complete, you were sure to be out of the stall and washing your hands by the time Kelsi was out doing the same.
"Hey, ma'am..." You say, modestly. "It sounded like you were changing that man's diaper. Why is he here in the girl's bathroom?" You ask.
Kelsi reacts a bit offended, at first, at the inappropriate question. But, regarding you as a child who wouldn't know any better, she answers.
"My friend here is special, and he thinks and talks just like a baby, even though he has the body of a grown-up." She explains.
"Ohh, so is that why he wears diapers?" You ask, drying your hands on your pants.
"Mhm." Kelsi tells you, taking Randal's hand.
"But... isn't he embarrassed? That a girl is changing his diapers?" You ask.
"Uh... no he's not really, he thinks just like a baby and so he doesn't worry about stuff like that." Kelsi answers, increasingly uncomfortable.
"But!" You fuss, playing the part of a child despite your retained adult mind. "But what if YOU had to wear diapers and a boy came up and changed it for you?"
Kelsi glares at you.
"...I don't know, honey. Look you should probably go talk to your mom or dad about stuff like tha--"
"Because I can make that happen." You interrupt, pulling out the device and activating it on her--regressing her mentally.
"What are you... I don't... I..." Kelsi mutters helplessly as she loses all of her intelligence, knowledge, experience... until she is stuck sitting there on the bathroom floor, an adult with the mind of an infant, wetting herself. You didn't keep "reality" switched on for her like you had for Randal, and so no adult diaper emerged to keep her protected.
You turned the device back on yourself and grew back up again. Your hair cut back down and you were just as you had been a few minutes ago. After that, you finally hit the "reality" button, and everything updated to reflect the nearest logical scenario. Kelsi's diaper bag flung itself into your hands and changed a bit in design, then it suddenly became bigger and heavier. You took a peek inside, and saw that it contained twice as many diapers as before. Suddenly, your mind filled up with years of experience in special-needs caretaking.
Kelsi's accident did not change, however. And so you needed to pick her up, and take both her and Randal out of the women's restroom, and over into the men's. There, you placed Kelsi on the changing table and removed her pants. You then removed her wet panties... the last pair of panties she would ever wear. You took out some wipes and cleaned off her clean, naked private parts (her genital area kept smooth thanks to your shaving skills), powdered her up and then put her in a big white adult diaper. And considering that Kelsi now had the mental status of a 20-month old (with Randal being 29 months), this would be the first of many diapers she would need to wear.
You put Kelsi in a pair of spare shorts, threw hew soiled jeans away and took the both of them out to continue their trip around the mall. This time, Kelsi joined in with Randal in giddily enjoying the colorful lights. A few hours later, both of them were thoroughly tired and you packed them up in the car to head home. Your vehicle had transformed into an SUV, and you drove it smoothly through the city to your home which had become much larger.
After dinner, Randal had an issue of smelling pretty badly. You took him over to the changing table in the bedroom and opened his diaper up; revealing a big wad of mess smeared all around his bottom, some of which having gotten on his penis as well. Breathing conservatively, you took wipe after wipe to the problem until Randal was left spotless. By that time, however, he had also been worked up to the point of having a giant erection, pointing straight up at you. You won't be able to get a diaper on over him like this, and so you thoroughly sanitize your hands and get to work on making Randal ejaculate. You place your left hand over his scrotum and constrict your right hand around the base of his shaft. You rub up and down, first slowly then faster and faster. You work your way up to the tip of his penis, rubbing his skin over it repeatedly. After about 10 minutes of buildup and non-verbal moaning, Randal starts to breathe heavily as he grits his teeth and closes his eyes. To swiftly push him over the edge, you lean in and press your lips against the tip of his stiff little penis. Assured that you had cleaned him very, very thoroughly, you lean in further and slide his dick into your mouth, and begin suckling away as you continue your rubbing. Randal gasps, and his semen splurts out of his little penis and floods the back of your mouth. Oh my, that was in all likelihood very same orgasm he was saving up for Kelsi. But now... not only will he not be having sex with her, considering his lack of social skills, he will not be having sex with any girl ever again. He will be reliant on you, his older male caretaker, to administer his sexual release. Dependent on another man just to be able to cum. And for the rest of his life, too. Just as soon as you had gotten him cleaned up again and back in a fresh diaper, Randal began to drift off to sleep and soak his diaper all over again. You hadn't even gotten him off the changing table, and it was already time to untape and replace. This time trying to minimize how much you wipe his soft, overstimulated private parts.
Tucked off to bed, you headed back to the living room to see Kelsi squatted over on the carpet. You hear her grunt and moan, then sigh in relief. Already, you can smell the faint wafts of her diaper. You watch as she is about to sit down...
"Wait, don't...!" You reach out, trying to catch her.
Unfortunately, Kelsi does not know what's good for her. She plomps right down on the floor, squishing her fecal matter up and down the innards of her diaper, and setting a wild scent up to your nostrils from above.
"Oh well, you needed a bath anyways." You said, picking her up and turning her around to assess the damage. "Hooh! You did a big dumpie in your lil' pee-pee stuffer, now didn't you?" You tease, patting Kelsi's bottom. She giggles and coos, blowing spit bubbles which pop and drip down her chin. A few hours ago, this woman was an undergraduate interning at a major law firm... now she didn't even know how to use a toilet. She just laid there and giggled, all the while the mess from her bottom started sliding forwards.
Taking a closer look, you saw that she had wet herself as well. A while ago, in fact. The pee had gone cold, and only now freshly warmed up by her bowel movement.