https://www.nhs.uk/conditions/selective-mutism/
Many children become too distressed to speak when separated from their parents and transfer this anxiety to the adults who try to settle them.
If they have a speech and language disorder or hearing problem, it can make speaking even more stressful.
Some children have trouble processing sensory information such as loud noise and jostling from crowds – a condition known as sensory integration dysfunction.
This can make them “shut down” and be unable to speak when overwhelmed in a busy environment. Again, their anxiety can transfer to other people in that environment.
There’s no evidence to suggest that children with selective mutism are more likely to have experienced abuse, neglect or trauma than any other child.
When mutism occurs as a symptom of post-traumatic stress, it follows a very different pattern and the child suddenly stops talking in environments where they previously had no difficulty.
However, this type of speech withdrawal may lead to selective mutism if the triggers are not addressed and the child develops a more general anxiety about communication.
Another misconception is that a child with selective mutism is controlling or manipulative, or has autism. There’s no relationship between selective mutism and autism, although a child may have both.