Check with the school to see if the local fire companies put on fire prevention activities in the school. If they don't, perhaps you and other parents can help the school to coordinate such a program. The local fire department might work with your child on an individual basis.
If you believe this is beyond the normal interest -- and none of these suggestions work -- I would strongly urge you to find a professional licensed counselor who specializes in children's issues. I know you want to protect your child, your home, and your family from any harm that could come from setting fires.