In a talk at GDC a couple of years ago, Jesse Schell of Schell Games talked about ways to design family-friendly games, and one of his suggestions was to market the game in a way that gets the parents on board. He said things like newsletters and emails that notified parents about the good things that kids were doing in game was a good way to gain a parent's trust and convince them that their purchase was worth it. He also cited flexible subscription plans, and family plans in particular, as great ways of connecting parents, children, and even extended families in MMOs.
The free to play model is not without its problems for publishers either. Witness the demise of Wiglington and Wenks, which had to shut down because of lack of funds.