Hmmm... I was afraid that the system would be too complex/off-putting for kids that young. I'll reconsider. Thank you.

I DM'd for some 8 year olds while working at a summer camp once. I was using one of the 3e starter boxes that comes with a simplified rule book and premade characters. You also have to be okay with just ignoring some rules that may add confusion like attacks-of-opportunity.

But overall it went great, maybe too great, haha. Afterwards they'd frequently try to suggest that instead of any normal camp activities they could play D&D. The camp basically made a rule against it because too many kids got interested and you'd either have an unmanageably large game, or have to exclude kids from the game.

I think the 5e starter box is somewhat similar. I know it comes with a reduced rule soft-book with just the important rules and spells. I believe it includes premade characters too but I'm not 100% sure.

It's still moderately complex, but as with any of these games it can be delivered in language like "what do you want to do?", and then you walk them through doing that (along with accompanying dice rolls, modifiers, etc).

If you go this route, ask for what kind of character they want to play, create/find a pre-gen, and go from there (don't bog them down with character creation, -especially- if they want to be a spell caster). Don't worry about going into depth in the rule system beforehand, let it come up organically. Try to get a game with friends first so you know the rules, so you don't have to slow down to look things up, and be willing to adjudicate freely (as kids, especially, may want to do very unorthodox things).

All the usual DM/GMing rules apply. Make failures as spectacular as successes. Try to describe things in ways that are interesting, rather than just "you hit it for 8 damage". See if the kids engage. If they do, they'll pick up the rules as you play. If not, move on.

...and don't forget that Wizards has made the streamlined basic rules available online for free:

http://dnd.wizards.com/articles/features/basicrules

Like someone else said, a majority of the complexity in DnD is character creation and actual battles. If you have experience in it, it is a lot easier to get into. I would recommend that for first timers to stay away form spell casters, it gets complicated quick.

With that said, 5th edition DnD is pretty easy to get into, and it is a lot of fun!

It's fairly straight forward at early levels and you don't have too many abilities to complicate calculations beyond the base game rules, which you should be able to lead them through if they have any problems. 5th Edition is far simplified from 4e or 3.5e that most people remember playing.