Tandem Cycling - 6 year old stoker

We bought a Trek tandem last year - a pretty old model but it was in great shape with minimal miles. I don't care for it at all! I'm in the back and can't stand to not be in control. No problem - really! So, we're thinking of setting it up for our now 6 year old son. He rides on his own but for "family" rides he does a trail-a-bike, but that getting too small. Do I need a stoker kit (is that what they're called?) for the rear? What do they run? Nothing on ebay - i've looked.
Thanks for your help!

It would all depend on frame size and how he fits now.
If you put the seat all the way down just how far is he from reaching the pedals? at 6 he's got a good chance of needing only Crank Arm Shortners at the most. But this all depends on the tandem frame size. If Shortners won't get his feet on the pedals you'd need to go to kids crankset.

Stoker Kit examples (http://www.precisiontandems.com/catalogpartsweb.htm#childstoker)

There are a number of tandem dealers that can get you stoker kits.

If you have time, they kits do occasionally pop up on ebay.

I noticed this on Ebay- I'm not familiar with the details, so have no idea if it pertains to your situation:
http://cgi.ebay.com/Crank-Shorteners-for-tandem-kid-or-child-stoker_W0QQitemZ190160803347QQihZ009QQcategoryZ7295QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

Yup, we have an eye on them.

Well, just couldn't see spendning 70 plus dollars on used crank shortneres, but no worry. Found a used stoker kit on a tandem site and its being shippied to me as I write this. The guy is including the small handlebar, stem, etc. Can't wait.