Really? I genuinely thought a lot of the starter sets of D&D (all edtions) were aimed at a more family-oriented audience. I even saw the 3.5 edition box sets at Toys 'R' Us. There is nothing in those starter sets that says "No kids allowed!" Simple language, simple rules, and it gets the point across. Heck, they even made board games, puzzles, and action figures in the '80's.
Your just talking about "availability", I am talking about the sales pitch. I think if they were to push how family oriented the game is, and how great the memories and family unity that results form it can be, it would help push it into the market further.
I don't know about you, but I think I would have much more vivid memories about any D&D games I played with my mom and dad then I do have about our games of Monopoly, Spades, Chess, etc... IE I never played D&D with my parents.
I do play with my kids, and I do know they already have many great memories of our games to carry with them through their lives. Far more vivid then those I have playing board games, video games, and card games with my family when I was a kid.
I don't know about you, but I remember my RPG game experiencess, and what happened in them, far better then I remember my games of Axis and Allies, RISK, WoW, PS2, X-box, Heroscape, etc.... I have played with my friends, wife, and kids.