In a similar vein, here's ours:

Long vehicle Mk II by MikeDavis, on Flickr
Went for the left-hand extra chain, largely because the second-hand kiddiecrank came with the pedals reversed (RH body on LH axle) to let you run the ring on the left and I couldn't be bothered stripping them to swap them back
The cranks have grubscrews in the ends to stop the pedals unscrewing. Extra ring added to rear timing crank. Getting it all aligned is a bit fiddly. If starting from scratch I reckon the front drive option is probably easier.
Stoker is currently an average-height 5. Could definitely accommodate a shorter one, there's plenty of seatpost out. The kiddiecranks can't go any lower than they are without the cranks colliding with the outer ring/front mech below.
Takes a bit of faffing to get it all working, but well worth it. I reckon it's more future-proof than a childback tandem - when they grow a bit you just revert to the standard cranks. Can also take taller stokers as-is just by taking the pedals off the kiddiecranks and putting some back on the main cranks.