The fiercest animals are disarmed by a tribute to their young. The mother thanked her and invited her to sit on the bench by the door while she herself remained seated on the step. (126.96.36.199)
Pro tip: the quickest way to a parent's heart is to compliment their kids. Even nasty old Madame Thénardier get all squishy inside when Fantine compliments her daughters. It looks like Mme. Thénardier does have some family feeling—at least while her girls are young and cute. (By the time Gavroche comes around, though, it's nowhere to be found.)
"Will you look after my daughter for me?" (188.8.131.52)
Here's the thing: no matter how loving of a mom you are, it's not going to do your children any good if they're starving in the streets. Fantine has to find work and knows she never will if she's travelling as an unwed mother. For Hugo, this is one of the worst things about poverty—how it destroys families.
"My father […] was a humble, heroic man who gallantly served the Republic and France and was great in the greatest chapter in human history." (184.108.40.206)
You tell him, Marius. Here, Marius isn't afraid to defend his father in front of his grandfather—and this moment of family pride is a turning point for the guy, who leaves his life of luxury to fend for himself and, eventually, the revolution.
Another inevitable consequence was that as he drew nearer to his father, to the colonel's memory and to the things for which he had fought for twenty-five years, so he moved further away from his grandfather. (220.127.116.11)
As Marius becomes more interested in his father, he moves farther away from his grandfather. But you can't really blame him, because it's his granddad who said, "This family ain't big enough for the two of us." We're paraphrasing here, but you get the point.
"Because I have taught my children religion, Monsieur. I have never wanted them to go on the stage. They have been strictly brought up, and no backsliding!" (18.104.22.168)
Thénardier puts on an act in order to scam money from Jean Valjean, and one of the most hilarious things he claims is that he's tried to educate his children in religion, despite their lack of money. Since Thénardier is the most immoral man in this book by far, it's a miracle that Éponine and Gavroche managed to retain some tiny spark of humanity.
But then he heard his own spirit, become again terrible, roar sullenly in the darkness. Try to rob a lion of its cub! (22.214.171.124)
If you were a suspicious reader, you might say that Jean Valjean has an unhealthy relationship to Cosette, like feeling jealous at the thought that Cosette might be romantically interested in a young man (specifically Marius). Oh, sure, the book says he's jealous because he doesn't want to lose a daughter. But if you ask us, this puts a whole new spin on the phrase "family romance."
[Cosette] contemplated that family of birds, male and female, mother and children, with the sense of profound disturbance that a bird's nest imparts to a virgin girl. (126.96.36.199)
Um, okay Hugo. We can't say that we're familiar with this feeling, but we'll take your word for it. The point here is the Cosette—despite her virginity—has some vague longings to have a family of her own that seemed to be stirred up by seeing a bird's nest.
Monsieur Gillenormand at first went through every kind of torment, and then through every kind of rapture. It was with great difficulty he was restrained from spending all his nights at the bedside. (188.8.131.52)
Aw, looks like Granddad is a big old softy after all. When Marius gets shot in a French revolt, his grandfather spends all his time at his bedside, praying for him to recover. Deep down, Marius is Gillenormand's biggest reason for living. What's the point of all that money if you don't have any one to leave it to, right?
In this [Marius] was unshakeable, regardless of what it might cost, or the demands he might have to make of his grandfather or of life. (184.108.40.206)
Okay, family is important. But so is following your heart, especially when it leads you to the cute fifteen year old you've hardly exchanged two words with. (Okay, fine, she's a few years older by this point.)
"A family! But I belong to no family, least of all yours. I am sundered from all mankind. There are moments when I wonder whether I ever had a father and mother. Everything ended for me with that child's marriage." (220.127.116.11)
Without Cosette, Jean Valjean's family is gone. She was the only person in his entire life, and now he has to keep his distance to prevent his shady background from infecting her new life. From the way Valjean says this, we can tell that being "sundered from all mankind" is essentially the worst thing that can happen to a guy. (Remember, the whole book is about how we all need to love each other. You might even say that Hugo wants us all to become one big human family.)