The March sisters have an incredibly close relationship with their mother, who they call Marmee. Especially in the absence of their father (who is serving as a chaplain for the Union forces during the American Civil War), the girls dote on, respect, and love Marmee deeply.
In the opening scene of the novel, the girls are discussing Christmas and how little they have to celebrate or enjoy this year. They decide, rather than spending their money on themselves, to each buy something lovely and thoughtful for Marmee in order to make her happier. Each of them decides to buy something Marmee would appreciate but would likely not spend money on for herself. Even Amy, who buys only a small bottle of perfume at first (so that she can afford to buy something for herself, too), eventually swaps it out for a larger bottle. This example of the girls' thoughtfulness and generosity toward Marmee is evidence of the deep and abiding affection they have for her.
Further, when Marmee tells the girls that the Hummels have nothing to eat for Christmas and asks if her daughters will share their own food, the girls immediately go to it. They learn to behave selflessly, emulating Marmee in her concern for others. They also take to heart the lessons Marmee imparts—for example, poring over their copies of John Bunyan's The Pilgrims Progress in order to better themselves. The March sisters' respect for their mother is evident.