The truth is, most LDS families that I know have 3-5 children—higher than the national average, sure, but not THAT high.
In the hopes of clarifying some of these misconceptions, here is what we DO believe:
• We believe that the spirits or souls of all people (past, present, and future) are literal children of God. We believe that there is a finite number of spirits, and that all must have a chance to live in a mortal body before Christ can return—therefore, many LDS want to provide bodies for as many spirits as they are able.
• We believe that all people who have ever lived or will ever live will have the opportunity to learn the gospel. (We believe that after death there is a waiting time prior to final judgment, and that during that time there will be missionary work until all have heard, and been able to choose to accept or reject the teachings.) With that in mind, there is some advantage to bringing children up in the church, because that’s one more person who knows the gospel now and won’t need to be taught later.
• We believe that the command given to Adam and Eve to “multiply and replenish the Earth” is still in force. Therefore, we encourage couples to welcome children, and not to delay them for selfish reasons (such as ‘financial stability’ or finishing school). We believe that when we welcome these children to our families, God will help us provide for them. (As one of 9 children in a family with the single-income of a school teacher, I can attest that this is true.)
• We are counseled that it can be appropriate to delay or avoid pregnancy if there are health risks (mental or physical) for the parents, and that this should be considered prayerfully.
• We are asked to look to the Lord, and not to the world when making decisions about the number or timing of our children.
• We believe that children deserve to be raised in a family with both a mother and a father, therefore we encourage unwed mothers to either marry or allow the child to be adopted. We strongly support and promote adoption.
• For more information about the LDS stance on families, read The Family: A Proclamation to the World.
Hopefully that helps to clarify why it is that many of us choose to have large families. Sure, we are encouraged to do so, but nobody is laying down a law against family planning. It is always a personal choice, it's just that many of us choose large families because of the things we believe!
As arrows are in the hand of a mighty man; so are children of the youth.
Happy is the man that hath his quiver full of them.
~Psalm 127:4-5 KJV