How do you create a brand-new neighborhood within an existing one whose homes date back to the 1890s? That was the challenge facing the developers of New Crocus Hill three years ago. The 700 block of Fairmount and Osceola avenues was an anomaly amidst the stately, turn-of-the-last-century homes of Crocus Hill. The site never had been residential, but it had been a Catholic convent and school in a previous life. Another school, this one for children with learning and emotional problems called Bush Memorial Children's Center, replaced the convent in the 1960s. When its owner, the Amherst H. Wilder Foundation, ran into financial troubles in 2008, it put the land and the school's nondescript modern facility up for sale.