“Children are the future” is one of those clichés that ring true. We are all destined to grow older, die, and be replaced by a younger generation (provided that we don’t destroy the planet first, of course). But this cliché usually implies that our paths are already set, that these children will walk the well-worn grooves laid by their ancestors, to accept things the way they are. Talking with the young generation’s most vibrant and determined shows that millions will not follow, and are dedicated to the carving new paths for themselves and their fellows. “Letters from Young Activists” is a compendium of essays by these folks, to educate and inspire people of all ages.