Answer:
I would also say that when the family first hears the story of the monkey's paw, their curiosity is really about hearing a tale of magic and intrigue, almost like one who sits around a campfire and awaits a scary story, just for the thrill of it. After all, Mr. White complains early in the story about living so far out in the country that no one really stops by, especially on a night such as Jacobs describes, with its wind and rain. Truly, Jacobs sets the scene to be a scary story with the dismal opening.
When the Whites first see the monkey's paw, Mrs. White "drew back with a grimace, but her son, taking it, examined it curiously." Mr. White also takes the paw and examines it, though no descriptors are given about his reaction.
Once the family is in possession of the "talisman," they still treat the monkey's paw as if it is a joke, but when Mr. White makes his first wish, "a fine crash from the piano greeted his words, interrupted by a shuddering cry" from Mr. White, which frightens Mrs. White and Herbert. Mr. White claims that the paw moved when he wished, which causes the family to doubt their initial mirth at the story the soldier told. In the morning, however, they return to their disbelief.
By the end, when the wish of 200 pounds is granted in lieu of Herbert's death, and then the second wish seems to bring Herbert back to life, Mr. and Mrs. White both believe in the power of the paw, so much so that Mr. White uses his last wish to wish that Herbert returns to the dead.