Kids are a complication but not a wall. It’s hard to be friends with folks who are busy without kids let alone with them but the once a month lunch you go to get means the world to them. Sometimes you just have to be cool with hearing, “I can’t because…” a lot.
As for new friends you gotta go and do stuff, you have to put yourself in a place where you are just enjoying yourself around people doing a thing first. Those folks might have kids too but they have carved out this one evening to do their thing and you can be there to enjoy it with them and make friends.
Honestly I’m saying this a bit as an affirmation because I struggle with the same thing of not having a deep social pocket outside of friends who moved away or had kids