Last night I ran my West Marches game, and my second son, 6yo, had a lot of fun before he had to go to bed. This morning, he asked to play D&D again today. Well, we had some other plans (we did get in a game of the Dungeon! board game this morning, but that didn't fully scratch the itch), but now dinner has been ordered and is on its way.
After dinner, I'm going to pull out the old Dragon Strike game boards and use those for maps (6 year olds do better with solid visuals), and have them explore it with their WM characters. My older's PC is level 6, my younger is level 3, so I plan to use the 3rd level wandering monster tables and the BX/BECMI random stocking method when they enter any rooms/areas, and randomly generate treasure on the fly.
I'll use Google searches to provide visuals for monsters encountered, too.
We'll see how it goes. Should be fun!