In my experience of MN, most users who don't have children are on at night. Most of the users with children are asleep (or wishing they were) at this kind of time, so if you want to canvass the opinion of parents, this was the wrong time to pose this question.
But I'm a parent (and a night owl!) so I'll answer you. FWIW (I talk a lot of bollocks though, so don't take this too much to heart!)
My DD is almost 15. I have 3 very close friends who don't have children and a 4th who only had her (pfb) child 7 yrs ago this week.
The answer is we were all worried about how it might change our friendship back when I got pregnant.
It didn't ruin the relationships I had, but it DID change it. Yes, my priorities changed. I was bloody tired for 6 years (had a bloomin' early riser). Non parents don't understand the hell of being woken up and having to be awake and take care of someone every day or every other day for year after year after year. You just can't come out and play like you did. Esp if you are breast-feeding.
I stopped (or - at least - massively reduced) my intake of recreational drugs. I miss them!
I found DD fascinating and adorable. And although I understood my child-free friends wouldn't find it as interesting as I did, and I DID try and reign it in, I did and do burble about her, which isn't interesting for them. I'm sure they'd describe me as VERY boring. And in some cases, it's bloody painful (something I try to be sensitive to, but don't always get it right). It's impossible (and possibly rude/hurtful) to explain to a non-parent how amazing it is when your baby looks over, sees you, recognises you and their lips do this twitching thing they don't quite understand, and then they smile. They smile because they recognise you and they love you and you feel a gazillion miles tall. You can't say that to your BF who hopes to meet a man and for it to happen but it hasn't yet and she's 43 already.
I should say at this point, one of my good friends describes me as a "smug married" (she is single). I'm really, really not smug (could happily strangle him most of the time!)
I think the thing is, your life changes when you get pregnant and have a baby. Surely it should do. But if you're both sensitive to each other, and if you're prepared to spend time having conversations (eg, about the contents of a nappy, or how you managed to dupe your partner so you got 7 hours of sleep instead of 3) and love and support each other, the friendships can continue to thrive.
I should say, I have another BF. It took us 6 years to conceive. She and her partner got drunk and forgot to find the condom once, and she was pregnant. We are still friends too, but it was bloody hard at that point, because I was SO fucking jealous. We needed medical help.
AND there's a whole OTHER thing of relations with other parents.... An unexpected side effect of having a child was meeting other parents who liked DD/had a child who liked DD/(in a v few cases) liked us and DD was a follow-up thing.
When you become a parent, these relationships become very important (I think), because there are people you can share experiences with, ask "is this normal?" to (if you don't have MN, as I didn't). So, to an extent, you ditch the people you love for similar-ish parents or parents who your kids bond with because you can lift share to all the extra-curricular stuff or share worries with, etc. And, as well as lift sharing (which is huge, because you spend ALL your life driving here and there to drop them off and pick them up again), you can ask all those questions. Plus the kids love each other, which is lovely for them. And you can babysit for each other for free, which is great. And you just see them every day on the playground. You don't LIKE them in the same way you like the friends you've got as your BFs, there isn't the same CHOICE you have with your other friends, but they are a regular part of your life, so they see you at all moments and they get to know you quite well. You reach a certain stage of intimacy. And you can't avoid them.
BUT the one thing you can't do with those parents is shamelessly boast about your child. But you CAN do that with the ones who don't have kids, but they love you, so they'll let you do that. This is really, really, really important in my life, and i'm so grateful that K and K and R and previously J (but can't do J now because she's got a DD of her own) don't care enough that they're happy to hear I'm proud that DD got a speaking part in an assembly (or whatever). You can't say that to another parent, because their kid might have less than yours.
BTW, I'm aware this post sounds like a stealth boast about how popular I am. I should point out that have very few friends (maybe because I'm a parent, and def because I'm not very nice) and because of this, I stick like glue to the few I've got, so when I say "my 3 bfs" I actually mean "my only bfs!"