Oh I have lots of thoughts on this! I'm a single woman in my 30s. All of my closest friends have young children.
I accept that this is a period where I will need to do a bit more flexing in terms of meet ups. I don't mind that because I have wonderful friends who make me feel cherished in other ways. I know that it is temporary.
But I try to do it in a way that works for me. So I think before accepting invitation to children's birthday parties (as you're right, adult conversation is often impossible). And when I do accept a very kid-friendly activity (e.g. park) I go into it expecting that the purpose is to spend time with my friend and her children rather than expecting a proper catch up.
I also genuinely love my friends' children - I don't know if I'll have children and I get so much joy out of getting to know them and spending time with children generally, it's not something I'd otherwise get to do. I accept this might be harder if you don't feel the same. Also, they are the most important thing in my friends' lives - so if I didn't show an interest in them at all then I feel like our friendship wouldn't be moving with the times?
What I will often do is go to a friend's house, see kids for a bit for bath and bedtime and then catch up properly after they've gone to sleep.
I've also let a couple of friendships with second tier people drift. Not really consciously, but neither of us are really interested in going out of our way for the other.
I also try to be honest with my friends about my needs, I don't want to become a martyr and have the friendships not serve me. Last year I had a very sad event. All of my close friends stepped up, took the effort to come over my way, time to support me etc. No one suggested meeting with their kids in a park on a Saturday. Similarly, this year I have 3 girls trips booked with friends, who are now able to leave their young children for a couple of nights. I don't think these things would have happened had I been adamant for the past 5 years that only a Friday night supper worked for me.
Anyway, bit of a ramble, but this is how I navigate it!