As an 18 year old, it's a bit too early to think about getting married and having kids, but I've always liked the thought of having children, perhaps a boy and a girl (but nothing more than two kids - I wouldn't be able to support that). I don't know - I've always loved kids, been volunteering in activities where I teach elementary school students and even kindergarten students, so it really gets to me when I think that perhaps I'll teach and raise my own child and watch him/her grow like them.
Having someone look up to me and call me 'daddy' can be the most fulfilling thing in life. With a sweet lover and wife, I'd think we'll be okay.
And there's a saying about those that hate kids that wail on the streets. First of all, well, there's parenting, but my point is: "It's different when it's yours."
Also uh, I think the biggest argument with my future wife would actually be, well, naming the child. Some names don't go well with my last name (not the best ring to it), and if my wife's favorite name happens to be one of them, ohhhboy. We're going to be fighting for the best name.