What do you mean by "nonverbal"? Do you mean cannot utter a sound or has difficulty forming words?
I have a child age 10 who has Down Syndrome and although she can speak there are some sounds that are really difficult (as in impossible) for her to utter at this time. She has made a lot of progress though, probably because she started speech therapy really early. However, she happily chatters in her own "language" with her dolls :)