Consider whether you have the time and energy an infant requires, and whether your existing children are ready to deal with the reality of a baby in the house. You may end up deciding that one is enough. We'll be the first to admit that money isn't everything, but you sure do need some when you're raising a family. It's important to consider your work situation, too. That's why we want to be better prepared for the next one.
Money is a huge consideration because of childcare costs.
The other big thing is career. I stayed with my daughter her whole first year. I would like to do that with the second child, too. It already feels a little late to me. Unfortunately age is a factor, especially for women.