Choosing when and how many children to have is up to the husband and wife together with the Lord thru prayer and fasting. Heavenly Father knows what we can handle and our desires. If you think that you need to "live up your life" or should have a solid career first...well listen to the words of President Spencer W. Kimball.
"You did not come on earth just to "eat, drink and be merry." You came knowing full well your responsibilities. You came to get for yourself a mortal body that could become perfected, immortalized, and you understood that you were to act in partnership with God in providing bodies for other spirits equally anxious to come to the earth for righteous purposes. And so you will not postpone parenthood. There will be rationalists who will name to you numerous reasons for postponement. Of course, it will be harder to get your college degrees or your financial start with a family, but strength like yours will be undaunted in the face of difficult obstacles."
If we really are here to provide bodies for our brothers and sisters, we should know that we shouldn't postpone or take lightly the counsel given to us by our leaders. The Family: A Proclamation to the world states," The first commandment that God gave to Adam and Eve pertained to their potential for parenthood as husband and wife. We declare that God’s commandment for His children to multiply and replenish the earth remains in force. We further declare that God has commanded that the sacred powers of procreation are to be employed only between man and woman, lawfully wedded as husband and wife." God's commandment for His children to multiply and replenish the earth REMAINS in force. That means that we as a people should be getting married and choosing to have children.
President Kimball continues, "Have your family as the Lord intended. Of course it is expensive, but you will find a way, and besides, it is often those children who grow up with responsibility and hardships who carry on the world’s work. And, John and Mary, do not limit your family as the world does. I am wondering now where I might have been had my parents decided arbitrarily that one or two children would be enough, or that three or four would be all they could support, or that even five would be the limit; for I was the sixth of eleven children. Don’t think you will love the later ones less or have few material things for them. Perhaps like Jacob, you might love the eleventh one most. Young people, have your family, love them, sacrifice for them, teach them righteousness, and you will be blessed and happy all the days of your eternal lives."
- President Spencer W. Kimball (in an open letter to all young couples, found in the Ensign, June 1975)
I know that if we follow the counsel we have been given we will be blessed beyond what we can comprehend as we endeavor to follow the Lord in deciding when and how many kids to have.