Hello. I believe I can be of help to you with this issue.
Typically, none of these medications (SSRIs) effectively eliminate OCD symptoms, but modestly to 'moderately' reduce them. This means that: 1) most kids don't respond well to them, but probably about 1/3 do; and 2) the symptoms will be moderately reduced in many cases, but the OCD won't truly 'go away', and typically, the medications cannot 'cure' it.
These antidepressants all work about the same in terms of effectiveness---that is, one SSRI doesn't on average, appear to be superior to another. However, physicians have different experience levels with different medications and tend to prescribe 'equally-effective' drugs based on the profile of negative side effects. So for example, an important study in 2003 showed that a tricyclic antidepressant called chlormipramine works a bit better that SSRIs on OCD symptoms in kids, but the side effects were much worse to deal with. Now, the real focal point for treatment with OCD in kids is cognitive-behavioral therapy involving exposure, response prevention, relaxation/anxiety
management. A child clinical psychologist who specializes in anxiety disorders and uses these techniques will produce results as good, but usually somewhat better than medications alone. So the combination of meds and therapy is probably 'the way to go'. Also, since people can clearly LEARN new coping strategies for many, many psychological symptoms and problems, long-term, therapy is strongly recommended because 'pills can't teach skills'. Now, you've tried "occupational behavior therapy" but this isn't an empirically-supported treatment for OCD in kids, to my knowledge. Again, you want a clinical child or pediatric clinical psychologist.
I hope this information is helpful to you. Please let me know if I have overlooked any aspect of your original question. Please click on the green Accept button at the bottom of the screen. Thanks.