i've used, "is that the only explanation for (x happening)?" quite successfully with my anxious husband. granted, he's an adult, but his anxiety started in childhood and this is basically the only strategy that has broken through.

he can now pull himself outside the automatic negative thoughts long enough to list all the other possibilities, and then can examine the "most likely" vs. the "most extreme" explanation.

all the best, this really is a tough one.

Every Sunday it brooded and lay on the floor. Inconveniently close to the drawing-room door.