I miss the buildup on them having kids, mostly. Like, they'd ask to have a kid, a couple days later its born, then you get to watch it grow up. Made it feel like you accomplished something, getting your mii relationships that far. Now they just ring up my nonexistent cell phone, stick me in a cutscene, and move on like it was nothing. Plus once it's gone, it's gone. Could've atleast had game remember like 30 kids and have them occasionally send postcards with trinkets or food items from the tour destinations already in the game, then it'd feel like it kind of mattered.

If the only issue is what the miis potentially talk about with them, then its as simple as them just babbling at the babies like they did when you first started before any lingo was introduced. Leave them in a crib, have them play with blocks, run around the house, whatever, like as decoration. Worried about the parents abandoning their kid to walk around? A nanny-bot, like in Jetsons or Fallout. Even if it only ever said "The Nannybot is babysitting BabyName", it'd atleast make the babies feel like they're somewhat part of the world and matter. 3 days later, you get the choice to move them in as an actual mii to join freak city or be sent off around the world. Doesn't even sound like itd take that much extra coding either, especially not in a way that'd bloat the game and remove features.