Kids are serious decisions these days. You don't just pop them out and let them live on their own after 18.
Personally I think people won't know if they want kids until they are at least 30 years old. They won't know how wonderful kids are until they hit some serious trouble in life and they have no one else to count on, and they won't know if it make sense to have them until they are old and their spouses died, leave them all alone in the world.
It is not for everyone, and many people have them not knowing why. If you just want something cute get a puppy. If you want to save the world help your local foster kids program and mentor them. If you want a bond that is unbreakable no matter how bad things are, have your own biological kids, and raise them well after you know how to be a good role model.