#I'll make it so that Ryoma simply hides his identity from Shiro and everyone around him to protect him...

[onebloodsoakedlion]

What if Fire Emblem Fates had, instead of babyrealms, a timeskip much like Three Houses and you don't get to recruit the child units until the timeskip? Either that, or the parents raise their children IN the Deeprealms (if nothing else, it's a temporary escape from the war) and they end up looking like they would if we went the timeskip route.

As for justifying the timeskip:

Revelation: The player's army is forced to fight Garon because he ends up hunting down the Nohrian siblings to kill them for "treason" (real reason: it's a last ditch effort to stop the Hoshidans and Nohrians from uniting and stopping the Vallites), and THEN they try to enter Valla, but it's too late. They spend the timeskip trying to find another way in and the post-timeskip part begins when they do find a way in.

Birthright and Conquest: Timeskip occurs after the main plot and focuses on the player's army having to protect either Hoshido or Nohr from a direct assault from the Hidden Kingdom. Anankos won't be slain in either of these routes but he and his army would be repelled and unable to return for thousands of years to come.

EDIT: I really need to not post stuff like this when I'm not at home since I just keep leaving things out by accident.