I can't tell you how many women I've heard from today relieved, so relieved, to learn there's something they can do to help ensure their children will be gay.  I've heard from at least one pregnant woman stocking up on soy products. 
 
I'm currently organizing a support group for disappointed parents of straight kids, to be called PFOTS (Parents and Friends of the Tragically Straight).  In the meantime, here's some help identifying all the possible soy products potentially available to you parents hoping to bring into the world a beautiful lesbian woman or a young man who'll help clean up after Thanskgiving dinner without being asked.
 
For example, here's a nice list of foods made from soybeans.  Here's a helpful list of soy recipes.  Even if your kid turns out to be tragically straight, soy products will confer to him or her the following health benefits (according to the link above):  thyroid health, energy and workout benefits, menstrual health, cardiovascular health, bone health, hair/skin/nail health, memory benefits, antioxidant benefits, prostate health, digestive tract health, kidney health, thyroid health and fertility benefits (which undercuts the whole gay thing, I guess).
 
Then, according to this site, soy can be found in body care products, candles, cleaners, composite materials, crayons, diesel additives, fabric conditioner, flooring, hair conditioners, hair styling aids (kind of explains the whole hair dresser thing, eh?), hand cleaners (nurses and chefs?), paint removers, pens, polish, shampoos ('nuff said), solvents and tables/furniture waxes.
 
Yes, indeed, it's a soy world after all.   So clever of the right wing to recognize it's not about fluoridation after all. 
 
If all that doesn't work, I can only share my mother's recipe:  vintage Broadway soundtracks from the period encompassing the early 1960's or so, and later on, make your son an altar boy.  I found myself oddly at home in a basic black frock. If that doesn't work for your daughter, or if you're not Catholic, get her into playing field hockey.  Seemed to work well enough in my high school.
 
Good luck!  Break a leg (or as we used to say in the Gay Men's Chorus, "Break a nail!").