E.,
I say leave it alone. I've lost and gained a couple of friendships in my adult years for various reasons. One was due to us having kids and our friends not. We no longer had the same things in common. We still see them occasionally as I play softball with the wife, but other than that - we don't spend time together.
I was a childless friend for awhile (by choice). I went to the baby showers, visted the hospital and gave the gifts. In all honesty, as happy as I was for my friends, I really wasn't into their kids. It had NOTHING to do with the kids and nothing to do with my feelings for my friends. I just was never a kid-person. The idea of spending a Saturday afternoon/night at a kids birthday party wasn't on the top of my (or my husband's) list.
I lost touch with some friends due to this, but it was hard to maintain a friendship with them. Not having kids, it was hard for me to understand why they couldn't meet for a girls dinner or shopping or take a trip to Vegas with us. Selfishly, I didn't want to meet for lunch and have to deal with the distraction of kids. AND, being a Mom now I KNOW how much of a distraction it is with our boys.
Again, it had absolutely nothing to do with my feelings for my friends, but more that we didn't have much in common at that time. Yea, it's great when you're a Mom and you experience the "milestones". Yea, you want to share with EVERYONE but really, I didn't know what a big deal rolling over, sleeping through the night, babbling, sitting up, etc was. (Now I DO!!)
One of the things that my DH talked about a LOT before starting our family is that we wanted to be T. and Rich even after the baby was born. Before we became Mom and Dad, we were friends, siblings, children, employees and most importantly husband and wife. Although we are first and foremost Mom and Dad, we still work hard to be who we were before. And, although time doesn't allow us to do all we used to do, we try to maintain some balance. I spent yesterday with my (childless) sister at the Spa, lunch and shopping. I didn't bring up the boys at all - unless she asked. My best friend (childless) was in for the Holiday weekend and I took the afternoon away from my family and spent it with her at lunch and shopping. Again, I didn't bring up the boys but talked about topics we had in common.
So, my long-winded piece of advice is to accept the friendship for what it is and enjoy what you have with your friends. They may become parents eventually (we SWORE we were never having kids and then we SWORE only one...hell, I'm thinking about #3 now!).
Good luck to you.
T.