Also Hayto x Mozu might not be so bad, in the sense they look roughly the same age and you can mentally go "Yeah, they didn't do anything until they were 18+" Course that still involves pushing two children together and going "Go bang in a couple years." .
Though really Fates should have just had the child characters have their own postgame adventure. It's not problematic at all if the shota character has a child when the game advanced XX amount of years and they're an adult. Time travel only really made sense in Awakening....