I suffer from OCD personally and i know all to well those horrible thoughts that you just cant get rid of. You dislike yourself for thinking them but they just keep on popping up. This is the obsessive part of OCD.

It is interesting its happening again at the same time of year as last. I would look further into that.

I suggest you get your child into a psychiatrist and probably a pyschologist. They will be able to help you all further.

Hope this helps.