I think the distant future will still have families and the joys and trials of raising children. A two year old today has much in common with a two year old from a couple thousand years ago--as in needing constant supervision and care. Nap time, tantrums, sitting on mom's lap, playing. A child on a far future space ship will be no different. The time and effort of raising a baby to maturity will always be a concern for adults. So why not have child characters in a SFR book? Children raise the stakes--as much as a character does not want to die, they really, really don't want harm to come to their child.
When writing SFR there is something I always keep in mind. It wasn't the explorers, trappers or forts full of soldiers that tamed the west--it was the families, the women with children, who brought schools and churches, law and order to the Wild West. I envision much the same for the Diaspora Worlds.