We tried EMDR therapy with myself and Kitty and Bear to help with PTSD. My totally layman way of looking at it is that when you think of something traumatic, your body reacts as though you were reliving it (accelerated heart rate, tense muscles, adrenaline rush... all extremely unpleasant). EMDR doesn't make what happened go away, but it kind of distracts your nervous system from physically and emotionally reacting, allowing you to process the incident. You do not even have to talk to the therapist about the incident, merely bring it to the forefront of your mind.
I don't know how it works exactly though. My understanding is that once you have gone through the event then it is processed. You will still remember it, but it will no longer feel traumatic (no more night terrors, avoiding things that might be triggers, or other coping methods).
There are different techniques too. Our therapist used "TheraTappers" which are small oval shaped objects about the size of a key fob that you hold in your hands (or you can slip under your legs when your hands get sweaty). The tappers vibrate (like a pager) in your hands, back and forth between hands. You can control the speed of the alternation. Once when the battery was low it went really fast, and actually got Kitty all riled up. With me, sometimes the therapist just tapped with her finger in the palm of my hand alternately. I've heard some therapists can just move an object like a pencil slowly back and forth. The point seems to be the back and forth motion making the eyes move back and forth like REM sleep.
EMDR is especially good for people who have been raped, in a car accident, soldiers, or something else traumatic. Single events might only need 1-2 sessions. Years of extreme, prolonged trauma like what my children experienced could take years of EMDR therapy to process.
When my daughter tried EMDR, she was apparently not at a point where she could handle discussing her trauma at all, and had some major regression (some of this may have been because I led the sessions - and being used to attachment therapy - apparently forced her to stay focused past what she could process).
Our son tried it, but refused to actually participate so we dropped it. I used it a little, and it helped me calm down on days when I came to therapy and my normal life was overwhelming me(yes, that's every day).
All in all I recommend it for kids (and adults) with PTSD, even though it didn't really work for us (at this time).
Here is the explanation from EMDRIA.ORG: http://www.emdria.org/displaycommon.cfm?an=1&subarticlenbr=2
EMDR seems to have a direct effect on the way that the brain processes information. Normal information processing is resumed, so following a successful EMDR session, a person no longer relives the images, sounds, and feelings when the event is brought to mind. You still remember what happened, but it is less upsetting. Many types of therapy have similar goals. However, EMDR appears to be similar to what occurs naturally during dreaming or REM (rapid eye movement) sleep. Therefore, EMDR can be thought of as a physiologically based therapy that helps a person see disturbing material in a new and less distressing way.
I don't think anyone is sure why it works. One explanation is that EMDR is mimicking the bilateral eye movement that occurs in REM sleep (studies indicate that REM sleep plays a key role in memory consolidation.) However, traumatic memories do not get processed in the typical way. Instead of getting fuzzier over time as most memories do, traumatic memories stay vivid. EMDR helps to move the traumatic memory into the typical processing thus allowing the memory to "soften" in its recollection.