“Orphan Train,” Christina Baker Kline’s bestselling novel, is boarding the big screen.

Broad Green Pictures is developing a movie based on the book with Michael London and Janice Williams of Groundswell Prods., whose credits include “Milk” and the upcoming “Trumbo.” Christopher Monger (“Temple Grandin”) is adapting the screenplay.

Published in 2013, “Orphan Train” has sold more than two million copies in 35 countries. Its title is taken from the trains that ran regularly between 1854 and 1929 from cities on the East Coast to the Midwest, carrying thousands of abandoned children whose fates would be determined by pure luck.

Kline’s novel, set in modern day Maine, weaves together the stories of a 91-year-old Irish immigrant who as a child was shipped from New York City to Minnesota on an orphan train, and a 17-year-old who is on the verge of aging out of the foster care system. The pair develop an unlikely friendship when the teenager is hired to help clean out the older woman’s attic.

“‘Orphan Train’ is a poignant story with historical significance,” said Daniel Hammond, Broad Green’s chief creative officer. “It educates and inspires as it touches upon universal themes of family, friendship, loss, identity and the meaning of home. We are huge fans of the novel and look forward to bringing the story to the big screen.”

Asher Goldstein and Shary Shirazi will oversee the project for Broad Green Pictures.

Two-year-old Broad Green, launched by brothers Daniel and Gabriel Hammond, has focused mostly on developing adult-oriented dramas. Its first wide release, “A Walk in the Woods,” has grossed $28 million since opening in early September in the U.S. It opened “99 Homes” in limited release three weeks ago.

Kline was repped in the deal by Jerry Kalajian of Intellectual Property Group, Geri Thoma of Writers House and attorney Robert A. Strent. WME represented London and Monger. Monger was also represented by Rick Genow at Stone Meyer and Neda Niroumand at Niroumand Management. Christopher Tricarico handled for Broad Green.