I am not one be very opinionated about many things, but I do have something I would like to share with those of you who are married and in your childbearing years, lol. I don't think everyone is called to have lots of kids. I won't judge you if you only have one child, or if you have 20! It's not my place to judge how many you are supposed to have.
My main conviction is that you should PRAY ABOUT IT! The last few years, it has come to bother me when Christians don't consult the "Lord of their life" to ask how many kids God would call them to have. Yes, we'll pray about what college to go to, or what job to take, or who to marry, but not about something as eternally significant about whether to let God create life through us at all! We are so in control of it all, the decision to prevent, to attempt for pregnancy (and when we decide we want it, we want it right then!), and again prevent (even permanent decisions).
I know many newlyweds who just outright decide to prevent pregnancy for years, because that goes according to their own plan or goals (I was one!). I'm not saying everyone needs to have kids as soon as they get married; I just think they need to actually THINK about it and PRAY about it, instead of just making a decision assuming that's what they should do. And I know many married couples who determine exactly how many kids to have OR the spacing between their children based on their own wants or perceived capabilities to handle said children. Concerning capabilities, let me just say that even one child is HARD and more sanctifying than you know, so it is beyond my own abilities to even raise and train one according to God's will. I am dependent on HIM each day. (My kids could probably sing the song "Turn your eyes upon Jesus" because that is one of my regular songs that I sing aloud to get my mind in the right place on a hard or dark day.)
I don't think that the reasons mentioned above should be the only reasons to base our decision on. After having Emerson I was ready to have another when he was only 10 months old! But after having Lyla (who was a hard, sleepless baby) it took me a LOT longer to get to that point. And it was with prayer and conversations with Caleb that we decided to prolong the process.
But even though kids are hard on many days, they also bring so much joy and life. Choosing to bear children is being obedient to God's command to increase and multiply. It is also glorifying to Him in how sanctifying it is of us sinners.
"Behold, children are a heritage from the LORD,
the fruit of the womb a reward.
Like arrows in the hand of a warrior
are the children of one's youth.
Blessed is the man
who fills his quiver with them!
He shall not be put to shame
when he speaks with his enemies in the gate."
Final thought: His ways are higher than our ways and His thoughts are higher than our thoughts. Consulting only ourselves on this huge decision could be a mistake. Ask God what his will for YOUR family is. Ask him to make your heart and desires aligned with His.
(Side note: I do know many women who are unable to have children and I think, obviously, that adopting children would fulfill this calling as well. AND be fulfilling the job of the Church we are called to in James 1:27.)