I can't remember if I've mentioned this or not, but I have a six-year old nephew. Recently I ran a short game of D&D for him, using the 1981 Moldvay rules. It was fun for me, but I got the feeling that my nephew could have enjoyed it more.
I'm thinking of emphasizing the visual aspect, using minatures and a grid, maybe even during exploration. We were using legos, and he seemed to respond well to that, but it proved difficult to construct each area quickly as he arrived.
He seemed to enjoy combat most, though I stressed that there were other ways to solve problems. I think that I will provide more opportunities for combat, while still making sure he knows combat is not his only course of action.
I took the scenario from the original 3rd edition starter set, wherein you must rescue a unicorn from goblins. However I wrote pretty much the whole dungeon from scratch, utilizing the five room dungeon concept, but making the goblin lair part of a larger complex. He, of course, ended up going the "wrong" way, slipping by a patch of green slime to explore the rest of the dungeon. Hopefully I can run it for him again and he can track down those goblins and save the unicorn. But it's not a big deal if he goes "off the rails".
I'm still planning to run Monster Hill. I had a session almost lined up, but unfortunately circumstances forced me to cancel it. Hopefully I will be able to run it soon, however.