Fic Series Idea: Jason and Dick both get de-aged permanently in public at Damian's 13th birthday gala.
They both get de-aged to their 13th birthdays and have their memories from then. Both Zatana and Constantine confirm it's permanent but they also say there's something weird with the spell, it's not a simple de-aging spell but they can't figure out what the difference does.
Exactly a month after they get de-aged they find out. All the memories of the month after their 13th birthdays floods into their mind and the scars and muscle memory appears on/in their bodies.
The 2 Robins think it's cool but are secretly kinda scared because by the time they get to their original ages they'll be completely different people from both who they are now and who they became because sure they'll have their memories and bodies and muscle memory but they'll also have the memories of growing up again.
The rest of the batfam is horrified because this means Jason is going to have to re-experience dying and the pit and everything else and Dick going to have to re-experience all the shit that's happened to him. Being the "completely emotionally competent" people they are they sorta just decide to ignore that and resolve themselves to be better this time round (for Bruce and Alfred) and be good big-little siblings (for the rest).
Damian is also 13 and while it's a little hard to get past the fact that his Akhi and Richard are now the same age as him they become a terrifying trio especially since they can now teach each other a lot easier since they're the same age. Dick teaches them acrobatics and gymnastics and Jason and Damian are having a much easier time picking them up than when older Dick taught them. Jason teaches them how to interact with the people of the alley, victims, etc. and the dirty tricks he'd pull when in a bind as well as general street smarts like places to sleep and how to spot safe and dangerous people etc. which allows Dick and Damian to become a lot closer to the people of Gotham than they were before. Damian teaches them a bunch of stuff from the LoA so Jason and Dick become more effective fighters sooner.
At the beginning of every month Dick and Jason sit down with Alfred for tea and talk about the memories and scars they got the previous night while Alfred reminisces about that time. Sometimes the others join but not often, the most likely to join are Damian or Duke with Steph second most likely.
Obviously they can't go out as Robin so they pick new identities. Jason starts as Flamebird and then changes to Phoenix when he remembers he died. Damian gives Robin back to Dick and changes his name to Shadow.
They also get some new teachers since all of B's training will eventually come back to them. Cass teaches the 3 stealth at Damian's request. Tim and Cass somehow rope in both Lady Shiva and Richard Dragon. Jason finds out about the All-Blades because he accidentally summons them when looking for a knife to cut some bread and his memories of the All-Caste come flooding back and then he begs Bruce to get them magic teachers and Damian and Dick join him, Bruce eventually caves and the 3 become the apprentices of the whole of Justice League Dark.
Also the All-Caste isn't destroyed in this timeline and Jason brings Dick and Damian to it. Essence may or may not literally pass out because of how adorable the 3 are and they get some training there too.
By the time they're all 18 they're 3 of the strongest people on the planet. Dick is their moral compass and has basically become Nightwing but better this time. Jason is both completely different and the same, he's by far the most brutal of the 3 and isn't afraid to kill but if Dick tells him not to kill someone then he won't because Dick is the best out of the 3 of them at telling who could actually change and get help (pedos and rapists are still fair game tho). Damian is as good at stealth as Cass and has an affinity for shadow magic, Jason's penchant for theatrics also rubbed off on him, he also isn't afraid to kill but only does so in the most dire of circumstances. If the 3 show up together you know it's some really big threat but everyone also relaxes majorly.
Damian is the tallest of the 3 at 6ft 5 and has a similar build to Dick but slightly bulkier. Jason comes next at 6ft 4 (yes Damian makes fun of him for it but they both make fun of B for only being 6ft without the bat suit) and has a more similar build to Bruce but slightly stockier with larger muscles. Dick is the shortest at only 5ft 10 and has a slim yet highly muscular build.
Damian is the one that thinks and acts the most like Batman or an assassin in the field mainly using gadgets and stealth. Dick acts much more circus acrobat like by using his magic to create trapezes and whips and ropes and stuff. Jason makes heavy use of magic and is basically what if Red Hood had actual magic rather than just the All-Blades.