So this is the question of the hour when considering this new social phenomenon*of glbt folks rearing kids. The Vatican publicly noted in 2002 that gay parents are performing a 'violence to children'.
Fortunately, there has been quite a bit of research performed on the subject:
The American Psychological Association claims that there is no scientific proof that glbt parents do any harm to children. On the APA Website, Charlotte Patterson has written a summary of the research along with an annotated bibliography.
Another cite developed out of concern with Florida's adoption policy provides more background as well as another review of existing studies.
The most interesting possible problem from my perspective was mentioned in the New York Time's article and that is that the kids might feel more stress at school or be more likely to take homophobic comments seriously than their heterosexually parented counterparts. That article said that the kids were more likely to try to protect their parents by keeping the comments to themselves. It seems to me that this is more an issue for society than because the parents are somehow doing violence to their kids.
More to come on "living in two worlds."
*Many authors have observed a recent increase in childbearing among lesbians—the
"lesbian baby boom" (Mitchell, 1996; Patterson, 1992, 1994a, 1995a; Patterson, Hurt, and Mason, in press; Polikoff, 1990; Riley, 1988; Tasker and Golombok, 1991; Weston, 1991).