AU where Baelor, Brynden, and Maekar return from Redgrass to find that the Red Keep had been attacked. Jena, Dyanna, Daeron II, and Myriah are alright, their guards managed to get them to the safe room and defended it until order could be restored but Valarr, Daeron, and Aerion are missing.
The boys (Valarr and Daeron are both 6, Aerion is 3) had all been sneaking outta bed exploring when the attack on the Keep happened. They went rushing into the secret passageways and eventually popped out of an old tunnel under the ruins of the Dragon Pit. They were too afraid to go back and in their little kid brains they assumed everyone was dead, not helped by seeing smoke in the sky when they looked towards the keep.
Dunk (aged 16), doesn't follow after Arlan. Instead, he goes off running in grief and pain to hide in the ruins of the dragonpit, which was his and Rafe's favoured haunt. There, he finds the boys. They're terrified, but Valarr notices that Dunk's injured and asks if he got hurt in the attack on the keep. Dunk explains that he got hurt trying to avenge his friend who was murdered. The boys are horrified, but they help Dunk to tend his leg anyway.
Dunk asks what they're doing in the pit, they tell Dunk that they need to get out of the city. That it's not safe anymore, but they can't articulate why other than 'the bad men killed everyone!'. And Dunk doesn't really want to stay in the city either, given the Gold Cloaks killed Rafe. So, he just shrugs and guides them outta the city.
Aerion's blatant purple eyes and silver hair should have probably been a hint about their identity, but dragonseeds are not rare in Flea Bottom and Dunk just assumed he was a dragonseed. Same for Valarr and his silver streak and purple eye. It doesn't help that they all give him bullshit names. Valarr is Val, Daeron is Ron, and Aerion becomes Arry.
Dunk spends the next month or so quietly freaking out like 'oh my gosh, I just became a single father of three!!' but he's leaning in to it, you know? He wanted a family, and Rafe told him to go out and find a family, and he has. He is. He will.
Dunk teaches the boys how to forage for berries and things. He and Rafe had learned as a necessity when they just could not get any coin for any food in the City. They'd learned how to trap and skin animals from an old, kind ranger who had seen no harm in teaching them, and now Dunk teaches that to the boys, too.
They travel from village to village, earning coin from odd jobs here and there. Dunk helps to build a barn for a farmer, and gets enough coin for new coats and things for the boys, because the clothes they'd been wearing when he'd found them were good quality, but not made to stand up to the harshness of the road. (just assume they weren't wearing anything with dragons on it at the time of the attack)
A baker in one town gives them food and teaches them to bake in return for Dunk helping the baker's son chop enough firewood to replenish their stocks for the approaching winter. Passing hedgeknights teach Dunk the basics of sword fighting, but they're not willing to take on a squire, especially not one with three kids trailing in his shadow. Dunk learns whatever they're willing to teach him, anyway.
Daeron starts having dreams around the age of 10, Dunk packs them all up and heads to the Isle of Faces, because he's always heard stories about the Green Men. The spend the next nine years on the Isle with the Green Men and the small group of Children of the Forest that survive hidden there. Daeron learns how to quiet his dreams enough that they don't haunt his every waking moment. Dunk, Valarr, and Aerion all learn the arts of war from the Green Men. Aerion learns how to properly process his own emotions (it is a work in progress).
Eventually, Daeron dreams of a tourney at a ford covered in ash. There are dragons there that Daeron and the others need to meet... Daeron and Valarr remember their time in the big Red Keep. They remember being carried about by the men they called father, before Dunk. They remember the women they once called mother. The know that there is a chance these dragons they're to meet at Ashford are the fathers they long thought dead.
On the other hand, Aerion doesn't remember anything before Dunk. In his mind, Dunk has always been his father, and Valarr and Daeron his eldest brothers, that's just the way things are and have always been and he's fine with that. Still, if Daeron and Valarr are going to Ashford, then Aerion will go with them, because they're his brothers. He won't be separated from them. Dunk's coming too, of course...
They pass by King's Landing, all of them eyeing it warily, and trying not to get to close to it. In the Kingswood, they meet the party of Lyonel Baratheon, traveling to Ashford. Lyonel has visited the Isle of Faces now and again over the last few years and he's happy to see them. They agree to travel together the rest of the way to Ashford.
In Ashford, Baelor catches a glimpse of Valarr and rushes to follow after him. Seeing Valarr is like getting punched in the gut because Valarr reminds Baelor so greatly of himself, and of the boy his eldest son could have been... Valarr knows he's being followed, but not by who and he doesn't figure that out until he pops up at the Elm looking wide eyed at Daeron and Aerion, and they all turn to find Baelor there.
Baelor looks from the boy who could have been his son, to the boys who looks so much like his lost nephews and there is... there is no way this is just a coincidence, right? It cannot be. There's just no way! There's shouting behind him and he turns to find Maekar rushing to catch up with him. They'd left the Kingsguard far behind.
They're all just staring at each other, and then Dunk comes wondering back to the Elm like 'hey, I made new friends! This Apple Boy is so ni- uhm. Boys. Have we been getting into trouble?'
Valarr, Aerion, Daeron: No, dad! Dunk: Right. Why do I not believe you? Aerion: It's not even my fault this time! It was Val! Valarr: Well, fuck me, I guess, little brother! Aerion: You're the one who led them straight here! Valarr: I wanted back up to deal with whoever was following me! Daeron: Never considered myself to be backup. I'm not sure I like it. Leave me out of it next time! Valarr: Ugh, as if I was talking about you, Ron. I meant Arry and Dad! Aerion: What do you want me to do about it?! I'm not punching some princes for you. Dunk: Princes?!?! Daeron: You didn't hear the royal party arrived? Dunk: I was too busy being plied with cider. Sorry. Daeron: Ooh, was it good? Dunk: Very good! We've been invited to- Valarr: Can we please focus? Aerion: No, but if we keep going, I think the one that looks like me might burst a blood vessel! Dunk: Arry!!! Aerion: Oh, that's mean, right? Sorry! I'm working on being a better person! Valarr: Why am I fucking related to any of you?! Why did the gods curse me like this?! Daeron: Now who's being a little drama queen? (at a sputtering Baelor and a fuming Maekar) I am so sorry about them. But hey, on the plus side, it's nice to see you both survived. We weren't sure about that for awhile, actually! Valarr: Ron! Stop talking, you're just going to make things worse! Daeron: DEFINE WORSE, VAL?!?!
Next thing you know, Dunk, Baelor, and Maekar are all having panic attacks while the boys argue over whose fault that is... Eventually, it ends up being Baelor/Dunk/Maekar... and Valarr gets his own personal set of guards to keep him from running off to go become a Green Man for real because he doesn't wanna be king ever... (they all survive the Spring Sickness)