The Lubavitcher Rebbe says (in a long speech about "Family Planning") that
One of the strongest objections is fear of financial inability to support children. Naturally, parents want the best for their children, and fear of being unable to provide adequately is a powerful deterrent to having them. This is a genuine concern -- but based on an assumption which springs from a weakness of faith and presumptuousness. One who fears that he will not be able to provide is assuming that it is completely through his efforts that he does succeed. True, Torah requires that man work to provide for his family. But it is a primary tenet of Judaism that all success comes from G-d, that it is His blessings that give sustenance, not one’s own efforts alone. It is G-d Who provides for all of His creatures; another mouth will not overburden Him.
An appraisal of motives might be in order. Is it possible that the concern of financial limitations may be a rationalization for living in a particular lifestyle? Contemporary society demands a standard that is, to say the least, profligate. Is it possible that we have adopted indulgences as necessities and this causes the worry about financial means? It is time to assess priorities to avoid regarding indulgence of trivial desires as necessity and a reason for not having children.