“If you want to start any kind of change,” says Amlan Ganguly in the remarkable documentary “The Revolutionary Optimists,” “start it with the children.” Ganguly, formerly a Calcutta attorney, now devotes his life to working with slum children in India. Through his nonprofit organization Prayasam, he empowers kids to become agents for change, teaching them that their destiny is not necessarily poverty and struggle — that they can work together to change their fates.

The film, directed by Seattle-area natives Nicole Newnham and Maren Grainger-Monsen (and partially funded by the Bill & Melinda Gates Foundation), profiles not just Ganguly, but several children whose lives have been affected by Prayasam. Sikha and Salim are a pair of bright-eyed 12-year-olds growing up in a slum with no potable running water; every day, family members must spend two hours walking to and carrying water from the nearest tap, located in a distant neighborhood. Kajal, a preteen who works in a brick field and has little education, dreams of being a tailor and speaks longingly of saving her money (which, until recently, she didn’t know how to count) to perhaps buy a sewing machine someday. Fifteen-year-old Priyanka — a lovely dancer whose limbs move like flowing water — leads the Prayasam dance group and, despite her abusive family, longs to break the cycle of child marriage and poverty.

Change is slow, and “Revolutionary Optimists” is no fairy tale; Ganguly’s organization can’t save all of these children, and it takes more than determination to bring about a new water tap. But hope bubbles through the film, in seemingly small moments: Sikha’s mother saying that she’s determined that her kids will have more choices than she did; Salim beaming as he learns that he’s been chosen to speak before Indian Parliament about the struggles his neighborhood faces; a group of boys and girls happily playing soccer together in the sunshine, on a community field where, not long ago, girls weren’t welcome. It’s a tribute to the power of optimism — and to an inspiring man who’s changing the world, one child at a time.