Are you sure the ones with kids weren't doing playdates and things? I feel like there's often a gulf between people with and without kids.

Of course they didn't go drinking, they had to get home to take care of kids. Or, like me, they don't drink. They might still invite over other families to go hiking or camping or maybe even know other parents from school.

Not saying that was necessarily happening, but now that many more of my friends have kids (I don't) I see them do this all the time. They can't really hang out without a way to distract their kids. Board game nights are much more likely to connect than drinking.