My wife and I are getting towards the deciding point as well, and we've gone back and forth a few times.
We're both 28 right now, but just starting into a good section of our careers (Both of us just moved from software engineers into management). So we're both making a pretty bundle, we moved into a nice new ouse (not above our means, but not really below either), and are doing well for ourselves. As has been stated in plenty of journals, 35 is around the last age you want to aim for children, as past that point you start to have increased number of birth defects, etc.
So we're trying to figure out what our priorities are, and what we'd like to do. Too bad life isn't like a video game.. "Ok, didn't enjoy that life too much without kids, lets reload and try our early 30's again without the condoms".
On one side of the ring, weighing in at 9 lbs 3 ounces, we have Children.
We do not want our children raised by relatives, babysitters, child care, etc (as we believe we'd be missing a large point of having children). So if we do have children, one of us would need to stay home for at least the first few years (at least until they're in school full time).
Now we also both feel pretty negatively about the public school system, so we're also leaning towards home schooling. That would basically knock out the next 18 years for one parent if we have kids.
Financially we would need to make multiple adjustments. Unless we get very large raises over the next few years (possible?), we can't afford our house / insurance / cars / etc on one salary. Currently one salary would cover costs, but leave no room for wiggle (I'm too paranoid to handle having no wiggle room in a budget). So we would likely need to move, probably sell one car (we have a new VW Bug.. pretty fun car, but not practical), and downgrade our lifestyle in general. Our savings rate would also be sharply cut for somewhat obvious reasons.
Now we're pretty sure we could afford kids (and afford the time) in around 15 years (after RE), but we would be busting right past the age we could actually have them. We've mentioned the idea of adoption when we get a bit older, but who knows. That's pretty far down the road
In the other corner, we have the titan of financial prosperity, the demon of free time, the master of golf... childless 2 income family!
Without children, we certainly have a lot of financial bonuses. Two incomes going up, two maxed 401k's, etc. As we go along, we're getting better at cutting our expenses, paying down debt, etc. Other than our house, our expenses have been going down over the last few years rather than up. So I figure we'll be sitting pretty within a few years as we pay down our cars (excessive purchases, which we've both somewhat regretted), put extra towards investing, etc.
As I've mentioned to my wife (since I run the numbers), if we don't have kids, retiring isn't an "if", it's just a when. We're looking at a possible 40ish retirement, more likely 45 if we don't rush things, certainly 50, and what the heck would we be doing working at age 55 when we could be on cruise ships all year long?
And the winner is?!
No idea. We "think" we would like kids. We both enjoy when they're around. We get a little google eyed when a kid makes a cute face in a restaurant at us. We also both walk away when a kid is screaming at a family party, so who knows? (I think usually we're frustrated with the parent, not the kid). Anyway, it's a very tough decision. It's made more difficult by the fact of the time constraints. As I mentioned, we'd be perfectly happy putting off kids until our mid 40's, but that's not really in the cards. We might miss not having kids, or we might regret them (both very sad situations). Who knows?