How does Dickens present the Crachit family in "A Christmas Carol"?

With the presentation of the Crachit family, Charles Dickens dispels the notion that poverty makes people worthless and demeaned. He presents a sentimental depiction of a family, portraying their love and affection for one another as well as the harsh reality of their poverty.

In an effort to expose Victorian class prejudice, and inform his readers that poverty is no crime, Dickens presents a poignant scene with the Crachit family's celebration of Christmas. When the Spirit of Christmas Present takes Scrooge to the Crachit home where he witnesses the joy and excitement of the children and parents alike, Scrooge cannot help being drawn into their exuberance. This family is a loving one, filled with individuals of distinct and worthy personalities, especially Tiny Tim, whose little spirit is cheerful and kind, despite his misfortune.

The loving family of the Crachits becomes Dickens's defensive argument against the Poor Laws of England, in which families, like his own, were separated as parents were imprisoned for debt. Moreover, Dickens uses the scenes with the Crachits to argue against the prevalent theory of Thomas Robert Malthus in Essay on the Principle of Population (1798), who contended that population growth would supersede food supply, so the poor had no right to live if they could not contribute to the economy and sustain themselves.
Especially moving is Bob Crachit's telling of how Tiny Tim hoped people in the church would see him and recall that Jesus cured the lame and the sick. Even Scrooge is moved by this frail little boy and asks the Spirit if Tiny Tim will live; however, the Spirit informs Scrooge that without the necessary care he needs, Tim will die. He then uses Scrooge's own words about decreasing the surplus population, which echo those of Malthus. When an ashamed Scrooge hangs his head, the Spirit scolds him,

"Will you decide what men shall live, what men shall die? It may be that in the sight of Heaven, you are more worthless and less fit to live than millions like this poor man's child."

Then, after the meal in which all have delighted, they gather around the fire with chestnuts and fill their cups with the "compound from the jug." Bob Crachit makes a toast to Mr. Scrooge and suddenly the delight leaves the faces of everyone. Mrs. Crachit does not want to toast him, but Bob insists "It's Christmas," so she does, although adding some of her thoughts. The children, too, begrudgingly toast their father's employer. But, soon the gloom cast upon them by Scrooge's name is dispelled and the family joyous once again.
As the Spirit whisks Scrooge away, 

...they faded, and looked happier yet in the bright sprinklings of the Spirit's torch at parting, Scrooge had his eye upon them, and especially on Tiny Tim, until the last.

Truly, Scrooge is moved both by the love and happiness in the Crachit family despite their material needs, and by the goodness of all, especially Tiny Tim. whose little frail body does not impair his Christian charity and love for all.