Lolly Rachpaul is 12 years old and a Lego master. He lives in Harlem, where his older brother was shot to death in a gang crime. When David Barclay Moore’s new novel for young readers “The Stars Beneath Our Feet” opens, Lolly is angry and sad and doesn’t feel much like celebrating Christmas. But his mother’s girlfriend becomes a kind of Santa Claus when she brings home two enormous sacks of legos. The small plastic blocks may become a foundation to help him through life. “The Stars Beneath Our Feet” is the first novel by David Barclay Moore, former communications coordinator for Harlem Children’s Zone.