Conventional wisdom says that it's better for a marriage if the couple puts off babies for a few years. Statistics say otherwise; one of the strong predictors of a marriage staying together is if the couple has one child within the first two years and another within the next two. (Shotgun weddings excepted.)
I always doubted the conventional wisdom, considering that if God really thought a couple needed a few years of time alone he could have made women have a 22-month gestation time, like elephants. Without putting any "oughts" on it, or denying that there may be cases where it's better to put off children, I'd like to speculate on some ways in which babies do help a marriage, even a brand-new one.
Babies provide a greater incentive to work things out. Everybody has times when they don't quite get along in perfect harmony. Having a third person in the house who is totally dependent on your ability to work together is a tremendous incentive to keep going regardless of your momentary feelings toward your spouse.
Being a parent makes you a better person than you were. As a parent you have two choices: become more patient, unselfish, and flexible; or go crazy. Most of us alternate. These qualities help a marriage (especially the insanity).
Babies make your commitment tangible and permanent: Sure, you believe in the permanence of marriage. But the reality is, as long as it's just the two of you, you really could walk away. Once you have a baby, your very DNA has melded together, and you will go the rest of your life having a part of you being also a part of your spouse.
It's the ultimate vote of confidence in your spouse: There really isn't any greater way you can show you trust and respect a person than by making them the other parent of your child. I once had a young woman volunteer to me the information (I never ask such things) that she and her husband had no children because he wasn't really mature enough to be a father yet. I had to wonder what had made her think he was mature enough to be a husband.
Babies help you get to know each other better. I know, everybody says this is why you shouldn't have babies. We can't figure out why. Presumably by the time you marry you have gotten past sitting around and sharing your favorite colors. If you really want to know a person--their deepest fears and hopes; their childhood memories and plans for old age; how they react to two a.m. crises when they got to bed at midnight--there is no better way than to raise a child with them.
If people mean "know" in the more, ah, Biblical sense, then it seems the presence of a baby at least indicates you're on the right track.
Babies re-orient you from present to future. People without kids are much more likely to live life focused on the present: spending their time, energy, and money on things that have immediate payback. Once you have a baby, you face the reality that a part of you will live on after you die. You have something in the future to live for. You start visualizing yourself as a grandparent and great-grandparent and building your life and marriage with that future in mind.
Babies create interdependence: Independence does not contribute to union; that's why God made both believers to need each other in the Body of Christ and spouses to need each other within marriage. But young, healthy people without children remain as independent, as a practical matter, as they were before marriage. With children, they become interdependent: neither of them could effectively raise the child alone. When you really need each other, not just in an emotional but in a very tangible sense, your sense of togetherness grows.
Babies make life's trials less significant. Not less numerous, by any means. But babies have a great capacity for acting delighted to see you without noticing that anything is wrong. And they still need just as much care whether you feel good or want to crawl under a rock and hide. It's a great distraction.
On the flip side, there are statistics indicating that a lot of people's marital satisfaction goes down after having kids. It'd be interesting to integrate the two studies and find out what the correlation is between those who wait to have kids and those whose marriages diminish in satisfaction afterward.
But even if people who launch right into child-rearing have as much of a let-down after kids as those who wait--or more--I suspect what may be going on is this: Yes, kids hamper the candlelit dinners, spontaneous trips, and long soul-searching conversations that people associate with romance. But they build the qualities that make for genuine love and commitment and a happy life-long union. Sooner or later the rush of first falling in love is going to diminish. Having kids right away means that when it does, you have a deeper and truer bond already in place.