Bestselling author Jodi Picoult had a reading with her daughter Samantha van Leer at Brookline Booksmith on Monday evening. But hours before the duo arrived in Coolidge Corner, they stopped by Boston Children’s Hospital so that they could read their co-authored book, “Between the Lines,” to patients and their families. The book, which was van Leer’s idea, is about a fictional hero who turns out to be quite real. Picoult proudly told us that it was also her daughter’s idea to add the hospital visits to their book tour. “She said, ‘If anyone needs happy endings ... .’” “Between the Lines,” a young adult novel, is absolutely an upbeat story, says Picoult, who admits that her grown up hits, such as “My Sister’s Keeper,” might be too sad and serious for younger readers to digest. “Between the Lines” also has an open ending, so there might be a sequel in the works, she hints. Of course, that sequel will have to wait until van Leer, who’s still in high school, is finished with her college applications. “She has a day job,” Picoult said.