I love de-aged AUs especially around the Bats because they didn’t grow up around each other and never saw each other as very small children so when it happens, it's like getting slapped.
It happens to Dick and he reverts back to eight year old Dick, full of energy and feelings too big for his body. And of course, he’s fast as fuck and has no sense of morality giving quarter to the strangers in eccentric costumes trying to pick him up. He breaks Tim’s nose, bites Jason and pummels Damian to the ground, he’s untapped rage and he’s yelling for Bruce or Alfred. Bruce appears and little Dick scales him like a fucking tree, perched on his shoulder like a parrot and for a second, Bruce who had no idea what has happening, is like, oh, I remember this. Dick isn’t even sorry to have caused injury and havoc. He shrugs it off, “you fucked around and found out”
Everybody thinks child Jason will be difficult as fuck but no, he’s sweet as sugar. He gets de aged to maybe five or six. He laughs easily and genuinely, with none of older Jason’s snark. He wants Dick to play with him or wants to go where he’s going, he holds Bruce’s hand wherever they go because safe, he feels safe. And he starts crying when somebody starts yelling, burying his face into Bruce’s leg or hiding behind Damian because when his other dad yelled… Jason is only cheered up by a prospect of getting a story read to him or getting a very large hot meal and Alfred is like, nobody fucking touch me, because he forgot - he actually forgot how small and undernourished Jason was. When he’s aged up again, Alfred insititues a bi-nightly family dinner and Jason has to attend or Alfred is showing up to Crime Alley with a glock.
With Tim, he gets de aged to maybe nine or ten and unlike most kids, he’s not asking where his parents are or what’s going on. He’s practically swinging off of Jason, babbling about all the cool Robin moves he saw or begging Dick to show him how to do flips. He’s weirdly attached to Damian who in turn in devoted to him, I’m talking Tim sat on his hip 24/7 and fed a stream of animal crackers from Damian’s pocket.
As for Damian, he gets de aged until he’s maybe a year or two old. He’s throwing tantrums left right and centre, red in the face from screaming and crying for his mom or his nanny but Alfred seems to know what to do, he has that kid in a wrapper tied to Bruce’s chest or back. Because lets face it, Talia probably wasn’t allowed to baby her baby while he was that little. Bruce calls her to tell her what has happened and for a day and a night, Bruce and Talia get to have that life they were denied with their baby boy. Damian is salty as fuck when he gets aged back up, mainly because “i’m not a child” but partly because, he missed what it was like to see his parents like that.
But de aged Bruce? He’s six or seven, he’s confused because who are all these strange people im his house, where is is mom and dad? Alfred, where is Mommy and Daddy? And Alfred ages like ten years as he just scoops Master Bruce up, telling him that it is going to be alright, it's going to be just fine. Alfred can't move out of his chair for the entire time Bruce is de aged because Bruce Wayne was and is a Velcro child and Alfred is perfectly fine with that.