“One step at a time” is how Brigid Collins and Jim Stewart plan to create a bereavement center for children on the East End. They took a giant leap in that direction in October, when they secured not-for-profit status for Katy’s Courage Fund, named for their daughter, who died of hepatoblastoma, a rare form of liver cancer. The third Annual Katy’s Courage 5K race, which celebrates Katy and furthers her family’s progress toward their goal, will take place in Sag Harbor on April 13.