At the Branstens' modern white dining table, the family holds hands for their nightly ritual.

Arielle, 8 years old, says she's thankful for her late grandfather, Horace, and how funny he was. "I'm missing him," she says. Her third-grade pal, over for dinner, chimes in, "I'm grateful for the sausages." Leela, who works for an education nonprofit, and her attorney husband Peter, burst into smiles. The San Francisco couple couldn't have scripted this better. Appreciation for things big and small—that's why...