So she should just cave in and pop out a baby because he kinda wants a kid maybe? How about discussing things, pros and cons of both ways. What if she really doesn't want to have a kid and he only THINKS he does? Wouldn't he regret forcing her to be unhappy by making noise about it, or leaving her when if he just thought things over he'd come to peace with it?
If he deeply truly wants a child for all the right reasons, and she doesn't then yeah he should have the option of leaving. However, it really sounds more like he's buying into the hype that child=you being mature, which is NOT the case. I'd ask him if all those teenagers popping out kids are more mature for having those babies, if the uneducated people who can't feed themselves but have kids anyways, are they more mature? You can be an immature twit without kids, or with them. Having kids has nothing to do with maturity, it only proves that you have a working reproductive system. Maturity comes with how you handle life.

People say many different things...doesn't mean all of them are true.

No, I'm not saying that at all. What I see is him wrestling with something. She is perfectly happy without kids, but he appears to feel like he is "playing house" being married without them. I absolutely believe that they need to discuss this seriously as a couple. Lots of men (and women) wrestle with the want or need to procreate - some for the "right" reasons, some for the "wrong" reasons. But a great number of men do have a primal/biological need to seed the earth with their DNA. How deep his need is, I don't know. He seems to be attempting to illustrate his desire by using the Hebrew saying that he heard as he reaches to explain what he is feeling. Perhaps he hasn't yet defined for himself why he wants kids, but clearly children are on his mind. To have or not to have kids is a deal breaker in many marriages. We have no idea what was discussed between this couple before they tied the knot. But clearly it needs discussing now. If he finds that he is certain that he wants children, then like any one he will probably regret the loss if he doesn't have them.

So what I am saying is that both people in this marriage matter. For him it's the new urge to have a family and what ever that happiness entails, for her it appears to be an unexpected issue to take seriously and will require her to make some choices that would make her happy in the long run. Whatever they are!