D&D with kids! "Chasing Pigs"

I have taken my first steps into indoctrinating my children into the world of role-playing games and that of Dungeons and Dragons. I watch them "roleplay" with each other all the time in their imaginative play together. I heard many times, "Ok now I say, Back you foul beast!" as the oldest swings an imagined sword of fire towards my oldest who is pretending to be Slimer from Ghostbusters. He in turn says, "I've leveled up so your fire sword can't get past my slime armor." So, I know they have the imaginations. They have these basic pre-programmed ideas of fantasy, swords, of powers and of levels of monsters and of fighting bad guys. I figured it was about time to get them into RPG's, especially Dungeon's and Dragons.