Labour is so well rewarded that a numerous family of children, instead of being a burthen is a source of opulence and prosperity to the parents. (1.8.23)
In some countries, regular workers make such good wages that people have as many kids as possible to bring more money into their household. No wonder you read these old books about families with twenty children.
A young widow with four or five young children, who, among the middling or inferior ranks of people in Europe, would have so little chance for a second husband, is there frequently courted as a sort of fortune. (1.8.23)
Smith is so confident in the wages of regular workers that he believes women with lots of children should be prized by single men because the children will one day bring in lots of money as workers.
We cannot, therefore, wonder that the people in North America should generally marry very young. (1.8.23)
With wages so good in America, it's little wonder that people get married young and start having babies as early as possible. It's when wages and work conditions get bad that people start thinking twice about having kids.
Marriage is encouraged in China, not by the profitableness of children, but by the liberty of destroying them. (1.8.24)
Adam Smith shows some of his cultural bias when he talks about how people in China have kids just to kill them. It's unclear what his source is for this information, which leads us to think that he's probably just drawing on cultural stereotypes.
It might then not be worth any man's while to educate his son to either of those professions at his own expence. (1.10.91)
There are some jobs that just don't pay well enough for fathers to spend their money on. Smith believes that these fathers should just put their sons into jobs that'll make money. Clearly he's not a fan of the whole "Do what you love" mentality.
As a military officer submits without reluctance to the authority of a superior by whom he has always been commanded, but cannot bear that his inferior should be set over his head; so men easily submit to a family to whom they and their ancestors have always submitted. (5.1.40)
It's likely that a family will happily acknowledge the superiority of another family if that family has been elite for centuries. But if someone wins the lotto and starts acting all uppity, it's a lot harder to accept the idea that they are above you in society.
[But] they are fired with indignation when another family, in whom they had never acknowledged any such superiority, assumes a dominion over them. (5.1.40)
Like he said earlier, Smith repeats this idea that your family will probably be cheesed off if one of the neighboring families suddenly gets rich and acts like they're all better than you. That's because we're most likely to envy those who are most like us.
Among brothers and among sisters, the eldest always takes place; and in the succession of the paternal estate everything which cannot be divided, but must go entire to one person, such as a title of honour, is in most cases given to the eldest. (5.1.38)
In a family, the oldest brother has traditionally been the one who's gotten the family property when the parents die. Smith says that this has been the case because otherwise, the family's money would get scattered and diluted across too many people.
Among them, father is the appellation of a superior; brother, of an equal; and son, of an inferior. (5.1.38)
In many societies, the concept of father is so connected to leadership that people use the word "father" to refer to anyone who is above them in rank. They also use "brother" for an equal and "son" for someone beneath them. Haven't you ever been on the basketball court and heard someone say, "I'm about to make you my son"?
We should not call a marriage barren or unproductive, though it produced only a son and a daughter, to replace the father and mother. (4.9.18)
Smith says that one of the most important things for economies is constant growth, which means that two parents have to have at least two kids to replace them. Otherwise, the population might start going down and there won't be enough young people to take care of the old.