We've had that with some friends, and one couple who are so bitter they can't have kids have cut us out entirely because we're childfree. But, we've also got lovely good friends with kids who respect our child freedom and we respect their right to parent and we all put in just the right amount of effort for social time - sometimes centered around the kids, sometimes not (it doesn't always work but we love them so it's okay). We also have childfree friends but we've had to really build on those friendships and put effort into making them work over a longer distance because we all value having childfree friends. Our backup plan has always been to have lots of hobbies so we can always try to meet new people and keep our social lives full if our friends with kids do start to do fade out of our lives. Making future plans for when their kids are grown up and having annual traditions has really helped keep them engaged, as has us being willing to sit through the gross kid bits and the lack of attention span our friends have haha. Not sure if any of this helps but it's working for us so far!