My 8 yr old just started not sleeping too..."it's too dark in the room" and has been asking for more light though he has a fairly bright night light. My 5 yr old daughter sleeps with a nightlight and a dimmer light on her dresser. I go in and turn it down to very soft light before I go to bed at night.
I did have to show them what the shadows were and that there was nothing in their room but God and his angels. When my son was younger (about 2-3) we had our dog come in an sniff under the bed, in the closet, or wherever else my son though "monsters" were hiding. Our dog would wag her tail and snort throughout the whole home and I had her sniff in my ear so I could tell my son she said it was all clear. He would then get concerned about outside, but I told him monsters do not like cats or dogs so they would not dare come near our house. I know you should confirm a fear of monsters, etc. but my son insisted they were real and had to be dealt with so we dealt with it...thankfully, that was a phase too.
We now pray at night together for sweet dreams and we ask God if he has the time to come and sit with the children as they sleep as well as send their personal guardian angel to watch over them.
You do need to watch what the see or hear these days. I sometimes believe that even his video games which are age appropriate give him bad thoughts. I just keep confirming that there is nothing in the house that will harm them and they should pray again for God to come sit with them so they can have a restful sleep.
Oh, we also play soft instrumental music in the background or the local Christian station at night to void out any "scary" sounds...like our neighbors loud dogs or rap music :0)
Hang in there, it will pass.
J.