My friends who've gone on to have children have morphed into two broad categories: 'people with children' and 'full on parents'.
In the case of the former, yes they have children and they will feature in their conversation, but not to the exclusion of everything else. They also realise there's a limit to my level of interest. Yeah, I'm interested in what their kids are up to, but not to the extent that I want to hear about their every bowel movement or the minutia of their sleeping patterns. For HOURS on end. My friendships have largely continued as before, but obviously I see a bit less of them, which is fair enough.
'Full on parents' talk about nothing but their offspring with a martyrish undertone and how they've never known tiredness like it and 'just you wait'. I've felt like asking if we could try talking about something outside this tiny bubbles you've created for five minutes, take your pick: music, film, sport, politics I really don't mind' and would it be really too much to make a brief inquiry about what I'm up to at least occasionally?
In a few cases I've accepted that the friendship is on ice for a few years and may never be revived.