I'm someone who generally isn't buying FE games for their story, even if it's nice when one manages to be interesting. So when I saw the explanation for children in Fates, I laughed and moved on.
Honestly, I think Fates has the best use of the children mechanic, they fixed up the balancing from Awakening so that the children don't really outclass normal units, and while it's also a part of Awakening I really like that the children don't mess with existing playable units like in FE4(I'm not a fan of the game deciding if I can keep using a character or not). The only real downside gameplay-wise for me is that getting all of them without grinding isn't really practical, which messes with the OCD side of me, haha.
Tieing marriage to supports fixes the issue of they system being kind of invisible in FE4. Some complain about the sudden marriage at S rank, but that's more on the poor writing of the two games than anything else(and also not really any different from many supports that end in marriage in the old games). So the whole thing feels properly fleshed in the gameplay side of things.
Since I'm playing FE for the gameplay first, I can overlook the story issues for the improvements as a gameplay mechanic, but hopefully they can do better with the story if the mechanic shows up again
. Fate's story really feels like it was a disaster behind the scenes that I'm sure no one wants to go through again, so I'm fairly optimistic that we wont get a repeat of it.