Not necessarily. Intangibles like life enrichment and love are part of a rational analysis. If a couple is on firm financial footing, with enough resources to meet the immediate costs of childbearing and a secure belief that they will continue to bring in enough to cover the costs of childrearing, if the couple wants children it would make rational sense for them to have them immediately.
But parents have responsibility not only for their own basic needs, but for those of their children. See Maslow's Hierarchy of Needs; having children (which I agree is a good thing) comes at the "love/belonging" stage, meaning only after immediate physiological needs and safety (future well-being) are secured. No one wants to be in the position of being unsure how they will meet their next month's expenses; I can't imagine how horrible it would be for parents not to know how they would pay for their child's food/clothes/education/health care/etc. So of course it makes sense to wait to have children only until you can reasonably ensure you won't find yourself in that position. That's what I mean by a rational analysis.
Read Antoninus last post to me. The Maslow stuff doesn't apply...