Why do we have so many kids?

Imagine you are pushing your shopping cart through the grocery store with your three children. Someone stops and says, “What is it with you people who feel the need to have so many children? Don’t you think the world is crowded enough?” (The developer of this course has had that experience.) How might you respond in a manner that is both courteous and instructive?
What I have found is that typically people who ask these types of questions do not comply with an answer like: “God has commanded us to multiply and replenish the earth; you should be having kids too.”  Someone asking this might see themselves as intelligent or well educated, but we know that this is a very arrogant, ignorant question.  The book explains the fertility trends to be decreasing as time goes on.  A documentary called “The Demographic Winter,” explains some important issues behind this problematic phenomenon.  One of those being the inadequate amount of people to take care of the baby boom generation because of the decrease in fertility rates also referred to as a triangle effect.
This question can also be used as a missionary tool, depending on the spirit it was asked in.  For someone sincerely interested in why you insist on having many children, you might give them an answer referring to your belief that we want to bring children into this world and teach them what we know to be true.  This might spark an interest in that person, as to what it is we know that is so important we would have multiple children to continue to pass it on.