I have no experience to back this up but I feel that you should avoid, at all cost, making a big thing about the instruments and controls unless asked. Make a point about the freedom of the air, no roads, no traffic jams (yes I know its not true but she`s only four). Show her a cloud (from the outside) if you can. Wait for a good viz. day so that she can see for miles and look into other peoples gardens. Can you actually go somewhere so that its a journey not a fairground ride? Is there someone to visit at the other end, someone she already knows of course?
Good luck anyway, I hope you both enjoy it.
Mike W
PS take sick bags, just in case.