Well, I meant rules light in the matter of number of rules just to get playing. D&D character generation (notwithstanding pre-gen chars from the box set) can literally take HOURS. There are too many boxes to fill, and too many things to look at. ANd that's just their end of it. You mentioned difficulty grasping everything yourself (yes, I know it was a first session thing). But sometimes it's easier to get 'on a roll' by starting out soft and working your way out to something as complex as D&D, which is quite simple in comparison to a number of other systems.
My advise: Look into some of the free rules-lite systems on the net yourself, see if you see something that grabs your interest.
I recommend looking at Risus and OSRIC for starters. OSRIC requires your D&D books for a few things (IIRC) but should be generally ok. If you like the d20 system (what is D&D 3/3.5 edition), you can look into things like Simple20, Microlite20 (my personal favorite of the d20 variants), or something like that.
My favorite system, is the PDQ system. It's very open ended and the 'core concepts' are free from Atomic Sock Monkey. I have their Monkey Ninja Pirate Robot: The Roleplaying Game book, and find it's absolutely one of the easiest games to pickup and go, and the setting for it is light and stupid, which might just work great for a bunch of teenagers.
However, if you decide D&D really is the answer - good luck. Read a lot. Ask questions. One of the better forums for such is
EN World. Good people over there. Oh, and did I mention READ A LOT. Part of being a GM is memorizing 300+ pages of rules. That's why I like lite systems that don't need all those pages of rules.