Why do people want children?

I know this may seem like an idiotic, cruel, or odd question, but I'm just wondering and confused. You may say that people want children because they want someone to share the love they have in them, but one may also purchase a puppy and do the same thing. I guess it's not the same for them and would rather have someone out of their own womb that they nurtured or something like that, but why? The key question to my question (if that makes sense) is wht? Yes, I know the answers as to the reason people want children, but why? I'm not saying it's weird for people to have children, because it's quite natural for most people...I just don't get of all things, some dream of having children their whole life. Is it instilled in society? Do people want a product of their love? Someone they can see themselves in? A baby they can consider their own, maybe subconciously selfishness? Hmm, I'm befuddled really. Sure, there are different reasons as to WHY, but I was just wondering. Thanks