I'm in my early thirties and adamantly childfree. I'm lucky enough to be in a long-term relationship with someone who brought up her desire to be childfree on more or less our first date. But I am not having too much luck with my friends from childhood and university - they all seem to be wanting kids, and learning of their pregnancies leaves me with a feeling of sadness. I don't hate kids and think no one should have them, and I am happy for them if they truly wanted this, but I also know what them having kids will mean - we are essentially putting our friendship on hiatus, and I still don't know whether waiting 10 years for the kids to be a bit more independent and not requiring as much attention will mean I suddenly have friends again, but somehow I very much doubt it. And I also don't want 10 years without other friends than my girlfriend. She is in very much the same situation, and while we are good at making the best out of not having kids and stressing about having them, we both would want to be able to hang out with good friends once in a while, both common between us, but also some that are exclusive to each of us.
My assumption is that this is quite common - so I am hoping someone would like to share some success stories in turning this situation around. :)
I think this makes sense. Firstly, respect your friends have children. Then, decide how to interact with them now that its what is happening.
If you want a regular, often relationship, having the ability to talk with the whole household on some level just seems sensible. They live there too; the kids are a person even if not a fully experienced one. Being an Uncle or an Aunt can be fun, or just be civil and honest. Ask stuff, field questions and above all don't be a dick.
The alternative is just to catch your friends when they're free. This might be rare or very occasional. That sucks but its their right to raise a family. The kids are dependant on your friends and your friends need to make sure they're OK. It requires patience and understanding. Possibly a little ingenuity.
In my experience, many parents will enjoy some time away from their kids every so often. If they want it, they'll find a way. And older kids will enjoy sometime where their parents aren't hovering over them. Either a weekly event or occasional times out might be possible to be carved out.
From my own Mother's words: your entire world shifts to revolve around your kids when they arrive. I would say you'd need to understand that and act appropriately.