When a child is hearing voices in his head it can be caused by emotional distress or other things.
Some other things besides emotional distress that can cause a child to hear voices in his head are bullying, loneliness, trauma or even after they have a fever or have had surgery.
It can be normal for a child to hear voices in his head.
I used to hear voices in my head as a child when I was 6 years old.
I was taken to a therapist and we discussed it but the therapist could find nothing wrong with me and said to me and my mom that it would likely just go away eventually.
The therapist was right because after 6 months or so the voices stopped being heard in my head.
It could've just been loneliness in my case as I was pretty lonely as a kid.
There's nothing harmful if a kid hears voices in his head for the most part and usually the voices will go away after awhile.