Suzanne found a group therapy program for children with the disorder called Brave Buddies at the Child Mind Institute, a nonprofit mental health-care provider in New York. A clinician there did an initial assessment of their daughter via Skype, and in February the family traveled from their home in Santa Monica, Calif., to New York, where they spent nine days doing individual and group therapy sessions.

This involved slowly ratcheting up the anxiety, such as introducing new adults into the room, so that the children could practice speaking in front of, and then directly to, new people. “The goal of the exposure is not to say, ‘That was easy,’ but to say, ‘That was hard or uncomfortable but I did it,’” said Rachel Busman, who heads the selective mutism program at the Child Mind Institute.