With Popsicle sticks and pipe cleaners, 10-year-old Justin Nicholson made grave markers for an extensive cardboard city that included a mayor’s office and a church.

Vivian Nicholson, his 14-year-old sister, drew swirls and painted rivers in shades of blue. It was all she could think about. Vivian and Justin had fled New Orleans with most of their family as Hurricane Katrina approached, but their mother had stayed behind and was now missing in a flooded city.

“My whole life was affected by water,” she said 20 years later. “It was surreal.”

After Katrina made landfall on Aug. 29, 2005, killing nearly 1,400 people and devastating the birthplace of jazz, art therapists from across the country descended on Louisiana. Bearing crayons, paint and sheets of white paper, they hoped that children would begin to draw what was too difficult to say aloud.

“They couldn’t talk about it because it would re-traumatize them,” said Karla Leopold, an art therapist who had traveled from California. “The fact that they can put something on paper and choose to tell you or not is safe.”

Their drawings of houses had recognizable doors and windows, but one of the most striking differences Leopold noticed was that the walls had been rendered as large triangles, not the square bases with pointed tops you would typically see in a kindergarten classroom.