KidzTandem, but since I already have both a Trail-a-bike and a Burley, this is the cheapest solution. Hooked up the Burley to the Trail-a-bike to the Mongoose. That is one of the reasons I got the Mongoose in first place, so I would have some gears to try to pull this off and it worked. Took my boys on a quick ride at the Monroe Rail Trail and we looked like a train. Kind of serendipitous when you think about it, pulling a train of bike related carriers on an old railroad bed. I had some guy take our picture but unfortunately both pictures that he took were blurry.
Here is a little ride video:
The Triplet from Mark on Vimeo.