I DMed my son in his first RPG experience last night just before bedtime. It ended up being one encounter- the party vs four ghosts in the Haunted Woods. The party encounters a friendly pack of wolves who lead them to the edge of the woods where four ghosts attack. Mom's archer, Tessa, and Dad's NPC wizard, Skytheen, helped Jack's swordsman/knight, Oko, defeat the ghosts. The archer was slimed, but in the end the party won. The chilly creepiness of the woods lifted and the trees whispered their thanks and then pointed in the direction the party needed to go to find the evil Frog Wizard they set out to defeat.
We played the very simple rpgKids game which was perfect for Jack's level of understanding and experience. It's a very nice little package with four great adventures, maps, character counters and everything needed.