I think it’s fair to not be interested in hearing about kids, but the reality is that may mean you aren’t interested in their life any more (and thus you aren’t interested in having a relationship with the person they’re able to be now). It’s likely to hurt their feelings if they mourn their past life themselves, but that doesn’t mean hurt is avoidable here. It’s also possible they love their new life and will not be bothered by moving on from their relationship with you, at least for a few years.