As for Carol, she was an orphan; her only near relative was a vanilla-flavored sister married to an optician in St. Paul. (1.2.8)
Carol lost both of her parents before the age of twelve, which gives her a different perspective on the concept of family than most people have. She also doesn't particularly care for her sister, and the two of them hardly ever see each other. This relation to family might help explain why Carol doesn't jump at the thought of having a bunch of babies with her husband right away.
"What's better than making a comfy home and bringing up some cute kids and knowing nice homey people?" (1.5.10)
Here you find the most common attitude toward family in a small town like Gopher Prairie. The folks here can't believe that Carol would want to do anything with her life except have babies and hang out with other people with babies. Not that there's anything wrong with that, necessarily, but hidden in this comment is the idea that this is the only right way to live your life.
She had so painfully reared three sons to be Christian gentlemen that one of them had become an Omaha bartender, one a professor of Greek, and one, Cyrus N. Bogart, a boy of fourteen who was still at home, the most brazen member of the toughest gang in Boytown. (6.1.9)
The book mocks the efforts of a woman like Mrs. Bogart, who tries so hard to raise moral men that she ends up driving all of them to lead immoral lives. She's in total denial about the whole thing, though, and continues to talk about the boys as though they were angels.
It was not her husband to whom she wanted to run for protection—it was her father, her smiling understanding father, dead these twelve years. (8.2.46)
Even though her father has been dead for more than a decade, Carol still thinks of him as the moral center of her life. He's the one she turns to for guidance—even though he's not exactly in a position to give any. Carol thinks it would be nice if she felt this way about Will, but, well, she just doesn't, and she can't force it.
Then, for three years which passed like one curt paragraph, she ceased to find anything interesting save the Bjornstams and her baby. (18.7.4)
For three years, Carol has nothing interesting in her life except her son Hugh and the Bjornstam family. So it looks like in some ways, she's able to take some satisfaction in the idea of family. But then again, her son might be more of a distraction than a source of fulfillment.
Miles had turned respectable. He had renounced his criticisms of state and society; he had given up roving as horse-trader, and wearing red mackinaws in lumber-camps. (19.1.2)
Once he has a wife and child, Miles Bjornstam cuts out his usual criticism of Gopher Prairie and tries to blend in more. He does this because he's now responsible for more people than just himself, and he doesn't want his wife or son getting mistreated just because people have a grudge against him.
For that autumn she knew that a baby was coming, that at last lie promised to be interesting in the peril of the great change. (19.8.8)
When Carol realizes she's pregnant, she celebrates. Of course, it's not like she's super pumped about being a mother; she's just excited that something new will be happening in her totally dull life. Newsflash: that's probably not a good reason to be having babies, though it's not like Carol actually chose to.
The first day she hated him for the tides of pain and hopeless fear he had caused; she resented his raw ugliness. (20.1.5)
When Carol first gives birth to her son, she's worried that she doesn't love him. Worse yet, she feels like she outright hates him and finds him ugly. She expected some sort of motherly instinct to take control of her. But it doesn't—at least not at first. It's something that has to develop and grow.
After that she loved him with all the devotion and instinct at which she had scoffed. (20.1.5)
After her initial wave of hatred, Carol realizes that she loves her new baby more than anything in the world. She even feels a natural motherly instinct—something she would have totally made fun of before feeling it herself.
Hugh was her reason for living, promise of accomplishment in the future, shrine of adoration—and a diverting toy. (20.1.10)
The baby Hugh means many different things for Carol. In one sense, she thinks of him as a vessel for her own accomplishments. But she also thinks of him as a toy—something that can distract her from the normal dullness of her everyday life. What happens when Hugh grows up and moves out?