My Step daughter, who is 4, shares a room with her mother.  In fact,
they sleep in the same bed.  This is very upsetting to my husband,who
questions the mother's sexual orientation.  I'm not sure there is
anything we can do about it legally.  Is there a law in California
about a child sharing a room or bed with a biological parent ?

It's done in many cultures, but it is weird in 21st century America. 
Here in NYC, there are subway ads, many in Spanish, advising parents
that this could be dangerous for the child (they could get squashed). 
When an ethnic colleague told me his baby daughter sleeps in their
bed, I gave him the "you have two heads" look.

By the way, even if the woman is a lesbian, I doubt she derives any
sexual pleasure from a four-year-old in her bed.

In short, no, there is no law against it. To the contrary, it's
becoming more widespread in the US.


Co-sleeping and the Media - By Linda F. Palmer, DC
..."The New York Times recently took the opportunity to provide us
with some great news from a new study: Cosleeping in the US has
doubled since 1993 --- from 5.5 to 12.8 percent..."


Consider this:

The Family Bed - by Tine Thevenin
Synopsis ©1998 by Meryn G. Callander
http://www.thewellspring.com/Cat/Adult_books/family_bed.html
..."That children sleep with parents is considered by many to be
indecent or immoral. Yet in spite of our society's preoccupation with
separate beds and bedrooms, supposedly to "guard" children and give
them a moral upbringing, sexual promiscuity among teens and adults is
rampant. Thevenin points to studies which indicate that a strong
interest or insatiable craving for sex may be the indirect result of
minimal physical contact received in infancy, an inner drive to repair
the damage of too little bodily stimulation during childhood. The
child who has been held and caressed by parents does not need to use
sex to satisfy that early need..."


Co-sleeping
http://parenting.ivillage.com/baby/bsleep/0,,429t,00.html
..."Should we let our child sleep in our bed? Not long ago most
child-care experts would have answered with an emphatic "No!" and
maybe even "Under no circumstances." Now the answer is more often "Do
what feels right for your family." There are a growing number of
experts who are telling mothers that they can do what they feel is
right for their children without fear of "ruining" them! This includes
co-sleeping, also called shared sleep or the family bed. Noted
child-care expert T. Berry Brazelton, M.D., reconsidered his ideas
about co-sleeping after hearing from parents on the issue. In a June
1979 article in Redbook he said, "When I advised against bringing
children into their parents' bed in an earlier article, I received
many letters from parents who felt that sleeping alone is a custom our
society unreasonably demands of its small children. I was impressed
and have learned a great deal from the letters that expressed this
point of view. I hadn't realized how many parents did NOT believe in
helping a child learn to sleep alone at night. Their letters and their
arguments made me reevaluate my rather rigid ideas on handling sleep
problems in our culture..."


Times have changed. Your husband's discomfort with the idea of
co-sleeping does not make it wrong, and the fact of his discomfort
certainly doesn't make the Mother a lesbian (or worse, a pedophile!).
I can understand his feelings, but he must not voice his concerns
about her sexuality to her. She would be appalled, I assure you, and
it would not help the situation at all. She would dig in and DEFEND
her right, and this would put a strain on the family.

I'm not posting an official answer because I know this information is not welcome.

You can find out more about this by searching Google for "Family Bed"
and "Co-Sleeping"

~~Cynthia

Sleep sharing is actually advised by some child rearing experts, like
William Sears (http://www.askdrsears.com/). I don't think it has
anything to do with sexual orientation.

See specifically
http://www.askdrsears.com/html/7/T071000.asp