Is it possible that they have selective mutism? Selective mutism (SM) is a severe situational anxiety disorder characterized by the inability to speak and communicate in certain social settings (school, work, parties, everyday errands, family gatherings, etc) due to severe anxiety. They are able to speak and communicate in settings where they are comfortable, secure, and relaxed, such as at home. Sometimes, SM can be caused by a speech impediment such as a stutter. In these cases, the stutter causes such severe anxiety around speaking to the point of SM. It may help them to learn sign language. It’s really good for people with SM to have a way of communicating their needs. Just know, Selective Mutism can affect nonverbal communication too, so they may not be able to communicate by signing. I actually have SM myself, so feel free to ask any questions. The subreddit r/selectivemutism is also a great place to learn more about SM from other people’s personal experiences with the disorder.