Downtown neighbors and friends are springing to the aid of Birgit and David Anderson of Battery Park City following a devastating diagnosis of leukemia for their 4-year-old son, Kai. The child’s hope for survival lies in finding a compatible donor of transplanted bone marrow. On Saturday, May 2, Kai’s school, Montessori School of Manhattan, 53 Beach St. in Tribeca, is hosting a bone marrow drive where potential donors can be tested in seconds with a simple swab of the cheek, inside the mouth.

The drive, between 9 a.m. and 5 p.m., is timed to coincide with the Tribeca Film Festival’s Family Festival, a street fair that draws thousands of visitors to the neighborhood. Those who cannot attend the drive can request a test kit at www.HopeForKai.com. Donations to help cover medical costs can also be made at the site.

The need for that help is all the greater because Kai’s father, David, is also being treated for a form of lymphoma.

“The Andersons absolutely need your prayers, kind words, home-cooked meals, practical assistance and generous donations for the enormous medical costs ahead,” Anna Grossman, who is helping to organize the drive, wrote in an e-mail blast to members of her parents network, Hudson River Park Mamas, and to others. Grossman is the founder of the group, now a network of 1,000 parents, and Kai was one of the original five children in the group when it began.

Greenwich Jewelers, 64 Trinity Pl., is also helping to raise money for the Anderson family with a silent auction of five pieces of jewelry. For information go to www.greenwichjewelers.com.