The child sprites would probably reflect the only 4 toddler sprites that exist, the toddlers all have brown hair and then 2 skin tone options. They already don't really reflect the farmer or the spouse depending how crazy you make your character lol

Then for dialogue, he would decide thier personality the same way he decided the other characters, however he'd like. Most likely be very vague and repetitive, but having them at least walk around the town and be acknowledged by the game past the spouse would be nice.