Mack Whittier, 8, right, and Leah Graves, 10, inspect huge spools of thread at Museum L-A on Thursday during a program about children who used to work in the textile mills across New England. The afternoon group of a half-dozen children with their family members was treated to a reading of Emily Arnold McCully’s “The Bobbin Girl,” a story based on 10-year-old Rebecca Putney, who worked in a mill in Massachusetts.