Even if you’re not a big fan of trends, fads, sweatpants, rolled mats tucked under the arm signaling hip and healthful purpose, gyms, alien Eastern religions, stretching-induced flatulence, cultural co-optation by whites, therapy of any kind, or sincerity generally, kids change everything, kids make it all right, kids doing yoga will bring a smile to your face, and so will “I Am Yoga” (Abrams, $14.95), a new children’s book about the practice by Susan Verde of East Hampton that hits all the right notes for today’s beleaguered young.