hi Briony, can I welcome you to the site and with his father coming back from a traumatised war zone isn't going to help your son with these intrusive thoughts, and now that they have started there maybe a tendency that they could develop even further, so that's a worry.
Intrusive thoughts are normally linked to OCD caused by anxiety, so at the moment there is your son, your husband and yourself beginning to feel the effects of mental illness, and if both parents are finding it difficult then it could be passed on their kids, not that they want this to happen.
If your son has been seeing the school counsellor then it would be worth taking him and yourself off to see your doctor and get them to refer you both to a psychologist, under the mental health plan, which entitles you to 10 free visits.
I would be more interested to see how it's going. Geoff.