as a result the child characters remain in their pocket dimension and do not join the main party.
That's from Fates/If, not Awakening. It'd make no sense for the child-units in Awakening to be in pocket dimensions in the first place. But I think you know that, given the tone of the section.
Fire Emblem Echoes: Awakening: IF
A remake of the fire emblem game that saved the series, which makes it the most popular and bestest. This story is actually changed by the interdimensional addition of popular characters from other games (wow).
You joke, but I legitimately believe that a remake of Awakening and Fates should be done at the same time and sold together, and whichever game is played first should lead to some fun interactions and bonuses on the other game.
For example, if you play Awakening first, then all of the Child Units (yes, all of them now, not just Inigo, Owain, and Severa) appear in Fates with bonuses, growths, and classes similar to what they had in Awakening, depending on who their fathers were.* Robin may or may not be recruitable later down the line, making it so that Morgan can be gained in Fates in a Paralogue chapter just like in Awakening. (Imagine a Corrin!Morgan and a Robin!Kana. Chaos I tell you! Chaos!)
Meanwhile, if one starts Fates first and then does the Awakening DLC, Corrin, their retainers (Felicia, Flora, Jakob, Kaze, that one old dude), Azura, however many royals are recruited will now be playable and romanceable in Awakening. So those who shipped Chrom and Camilla or Frederick and Camilla due to their supports in Warriors may now feel free to do so in the game. This will lead to some interesting Inheritance stuff - imagine, Malig Knight Lucina or Malig Knight Morgan!
Of course, due to this mixing of timelines and incarnations there'd have to be several characters who just can't support or S-Support each other once relationships are set in stone, and the games shouldn't let you build a family tumbleweed, but I think it'd be possible overall.
Awakening and Fates are the only games where this can work IMO because Fates more or less exists out of time or "the timeline." Lines in-game imply that it happens both before AND after Awakening IIRC.**
Obviously, this won't happen. Both games have a lot going on already, and a remake should work on highlighting their strongpoints and sharpening up those rough edges instead of looking at how to combine the games even further in a way that breaks them both. But it's a fun idea IMO, and one that would give these high replay-value games even more replay value.
*This wouldn't actually be too unique to them, as some pre-promotes like Reina and Flora possess three classes instead of the standard two. (Azura is weird in that she actually seems to have three, given that she will always pass down Troubadour to children who naturally inherit Pegasus Knight (with the exception of Jakob!Shigure) but she can't access the class herself unless she Second-Seals Elise.) The Awakening children would work similar to that. For example, if Severa's father was Stahl, then beating Awakening first would allow Selena to have access to the Mercenary, Pegasus Knight, and Cavalier classes. Similaryly to inheritance in Fates, if the Child Unit and their father share the same class (i.e. Severa/Inigo and Gregor sharing Mercenary, Owain and Lon'qu sharing Myrmidon), then it'll default to the next class they don't share. Things get tricky for the children if their father was Robin, and I don't have a good solution to that just yet. For Inigo, if his father was Chrom, I'm willing to give him either Archer or Cavalier to make up for with, with Rightful King/Ruler as a skill that he has but is unequipped. The real benefit of something like this is long-term unit planning for Fates 2nd Gen characters. A Lon'qu!Laslow can now pass down Swordfaire to Soleil without marrying Hana or anyone else who may have to give up a Second-Seal for the Samurai class.
**I may be remembering this wrong, as I can only find lines that hint at Fates being in the far past of Awakening, with Rhajat and Caeldori's Classic Mode Defeat lines hinting at their "next life" being their Awakening ones. Still, I feel as if I remember there being a line in the game or from the DLC where Ylisse is mentioned to be mythical to the Corrin and crew.