As you can imagine, this is something upon which the Church's stand has changed with time. I think the advent of widely available birth control terrified Church leadership. We believe in having children, always have, always will. We believe that's why the earth was created: so the spirit children God has already fathered can be born and live and die, becoming a little more like Him in the process. So if everyone can keep living like they are, but no one gets pregnant, all creation is for naught.
It turns out, however, that many people want to have kids, and that being to space them out and have no more than you can feed is a good thing. The official word can be found here. In a nutshell: Kids are good. Having them at the time and under the circumstances that's best for your family is good. As for expectations, we're expected to do the very best we can, whatever that may be.