Dear L.,
I have a nine year old son that has had some similar fears. I talk to him about my own childhood fears and imaginings and how our imaginations can scare us and that there is always an explanation for what we think we see or hear, ie., reflections, wind, shadows. There are some books out there for kids on the subject too. Your librarian should be able to help you find some. I also help him to realize that such fears and imaginings are a normal part of growing up, but that we have to overcome them as part of growth too.
We believe in God and that we are always under His care and protection and that we can call on Jesus and our Guardian Angels and our Blessed Mother Mary to always help and protect us.
Finally, if he is really scared and in need of sleeping with me, he can. I do the above helps to give him courage and to help him get past the sometimes scarey stages in growing up.
For you and your hubby, remember that this is just a normal stage and it too shall pass. Just love them through it.
Hope this helps.
God bless,
A.