Simon, I never did find any useful programs. Pete's suggestion is the best. I ride with my kids on local bike paths and footpaths, going to school, shops etc. As a general rule, I stay off the roads, except in very quiet streets. I am a confident and competent rider but still find it too hard to manage the kids safety on the road. Problems such as ensuring they pay attention and don't wander on the road, stay far enough out from parked cars but not too far onto the road, listening for cars from behind etc, all make me unwilling to try it until I am convinced they are ready.
The only advice I can really give is you need absolute consistency with the idea of stop, look, listen at EVERY road crossing. Otherwise you'll find the kids will sometimes go to cross a road without stopping or looking. I usually have them ahead of me so I can see what they are doing.
PS my kids, age 4 and 7 are now fantastic riders, have both been riding since they were 2, very competent in all situations but still not safe on the road unsupervised.