3 year old exhibiting behavior suggesting hearing things
Welcome to our discussion forums. 3 years old and hearing things would be extremely rare. The rate of schizophrenia / psychosis diagnosis for kids under age 13 is something like only 1 out of every 30,000 people.
Does the family have a history of psychosis / schizophrenia?
Two approaches that might be best for evaluation would be to contact the National INstittutes of Mental Health researchers who focus on childhood schizophrenia.
Another approach would be to contact an Early Psychosis screening / evaluation and Treatment center.
Here are some links and past discussions on this topic: