The thing I found the most surprising challenge was explaining the 'rules of the road' and some of the key hazards.
It's quite easy in principle to train the things that @Colin mentions, and definitely worth doing so that you have got the concept of a right turn straight before actually trying it on a busy road for the first time (as an aside, roads that seem quiet to you may suddenly seem busy when you have a free-range child on a bike).
I have the excellent Bikeability tutor's handbook, which is a waterproof book of pictures that shows how to do the various manoeuvres, and is great for explaining them. Happy to lend it to you.
Anyway, back to the rules of the road point. Having some basic concept of who gives way to whom, who has 'priority' and such like is worth it. I had some initial problems with getting Mini-Greenroofer to 'go', as she kept stopping every time she saw a car approaching us. In your case Mini-Chief will presumably have had the benefit of your running commentary while stoking your daily rides, assuming of course that he can see past you to the thing you're talking about.
The art of this is to pass on enough information beforehand that you're not issuing a continual stream of shouted instructions, because that can get wearing for adult and demoralising for child.