The answer to your friends' problem is very simple: either they got a bad or irresponsible husband (or wife as the case may be) or their husband (or wife) is still inmature and not having settled down, or may be they are forced to marry for reason that there is no need to tell!
In my own case, the 1st son came from half-accident; the 2nd boy was purely an accident. My wife did have some hesitation to keep the 2nd baby. Now, after 2 years and 3 months since 2nd boy was delivered, she told me that had she not been working, she would like to have a 3rd or even a 4th baby, because the joy and happiness that the two guys had given her outweighed all the pressure and stress that they brought with them.
As to myself, my character also changed after becoming a father. Before that I was cool to kids and had no sympathy at all to accidents happened to them. For instance, years ago, I did witness a little gal of age 7 or 8 knocked down by a KMB bus and her leg broken up. From her wound, I was sure that she would become a cripple even if she survived the accident. But I did not have any feeling on her at that time.
Worse still, I was so cold-blooded that I even regarded, in my heart, that she deserved for such 'punishment' for being naughty and running around on the road (for this I feel guilty after the lapse of all these years). I am now, however, a man with sympathy that I feel sorry and painful whenever I hear or read any accident in which little kids are involved.
In fact, I can predict that if, unfortunately, my wife has to make a choice between our two sons and me, she would definitely choose the former. I can also say with certainty that you will feel sorry for not having a child decades later; but it is already too late for you to repent by that time.
After all, whether or not to have child in your life is a matter of your own choice.