If you are reading this, you're a parent who is dangling by a thread and not sure how to reach your child/teen who is considering transition. I'm going to open this up with a bit of bad news, but you might also have some success if you follow my steps/advice.
So, pretty much, children and teens aren't going to listen to anything their parents say due to age, circumstance, etc. This is especially true if the parents are abusive, and if you are worried you might hurt your children or you have hurt them in the past, be a role model for your child/teen and get help. They will be more likely to get help and grow too if they see you doing it.
If you're a supportive and loving parent who has already worked through your own issues, read on.
The difficulty here is getting your child/teen to listen to you. The first thing I recommend in dealing with a child/teen considering transition is to act like a parent. I know that sounds more than a little bit condescending, seeing as I'm not a parent myself, but I can assure you that my childhood abuse was also peppered with moments where my mom and dad would let me get away with a lot of perks like staying up late or using the computer whenever I wanted just so I would keep quiet about the abuse. So, when I say it's time for you to be a parent it means to stop acting like a friend. I know that you want your kids to like you, and they should, absolutely. But they also need guidance and structured, but fair, discipline.
For me, I first really discovered F2T transition on the internet. I made lots of trans friends through the internet. I learned about F2T "passing guides" on the internet. I bought my first chest binder on the internet. I got lots of positive feedback loops from other transitioning adolescents on the internet (including them saying things like "your parents just don't understand/don't support you, you can sue them if they don't give in" etc). I saw my first dose of F2T pornography on the internet. I found a doctor that I could go see to give me hormone treatment on the internet.
Are you seeing a pattern here? I spent a lot of time on the internet, and the internet was paramount for delving me further into transition knowledge, in fact, that's the first thing that transitioners will tell you (on the internet) is to do as much research about transitioning and transgenderism on the internet.
So, do your kid a favor. Unplug them.
I realize they "need" the internet for school, as schools have pretty much made not using the internet freaking impossible. But you are a parent. Remember that. You have a responsibility for the health and wellness of your child. Prolonged social media usage has a negative impact on myself and many countless others. It can lead to feelings of isolation/alienation, while at the same time encouraging self destructive habits.
So, what do you do?
1. Go to a website which specializes in blocking certain websites from your computers. Use one that requires you to type in a password if you want to access certain sites. And then block the following sites: Facebook, Twitter, Tumblr, reddit, susans.org, ftmi.org, ftmguide.org, gendercentre.org, ftmmagazine.com (EDIT: 7/11/14, also include YOUTUBE in your list of blocked sites because that website is filled with a bunch of pro-trans videos). I would list mtf sites, however, doing a simple google search of "ftm" brings up a BUNCH of results for actual F2T people, whereas searching for "mtf" yields a bunch of results that have nothing to do with actual M2Ts. But do some digging around the internet and add those sites to your parental block filter too. Anything related to "ftm hormones," "ftm binders," "ftm packers," "ftm passing" etc, and you get the general idea. A google search for "parental controls internet" yielded some helpful sites you can check out for technical help with this crucial step. Parental Control Sites
2. Also, you need to be able to support your daughter, but if your child confronts you about your hesitations, simply tell her this: "if anything medically bad happened to you as a result of my consenting to hormone treatment for you, I wouldn't be able to forgive myself." Don't offer any further explanations. Hold firm on this. Repeat as necessary.
3. So, what do I mean by be supportive? Go ahead and get the "male clothes". If they want to use a new "male" name, be sure to say "that's a cool name for you, I think it encapsulates my brilliant and strong daughter!"
4. Break down gender roles and stereotypes as much as you possibly can. Ask your daughter what she thinks it means to be a man and what she thinks it means to be a woman. Remind her that in cultures around the world, these definitions change.
5. Make sure your daughter is safe at school. If there are any concerns of bullying, get that taken care of immediately. Report to authorities as necessary. Cyber-bullying is also a huge issue with today's youth. This is even yet another reason to get her unplugged.
6. Oh, and her cell phone? Get her a go-phone instead and hide her cell phone somewhere else (like at a friend's house, at your office, or anywhere else she can't go looking for it). If she doesn't have a smart phone, she won't be able to fiddle around on Facebook and all the other websites you blocked.
7. Delay the hormones as much as possible.
8. Meanwhile, encourage them to look at both sides of this issues, especially encourage girls considering transitioning to look at people who have been there who have legitimate complaints about health issues from hormones.
9. If possible and feasible, get them some counseling from an actual psychologist as opposed to a school counselor or a psychiatrist. The psychiatrist is only interested in pushing more drugs onto your child, so get them some real therapy. If they do need psychiatric pills, MAKE SURE THEY ARE ALSO IN THERAPY WITH A PSYCHOLOGIST SIMULTANEOUSLY. The pills are not the ultimate fix-it solution. You're not getting to the root of the problem if you're relying on drugs, even if they are prescription drugs for mental wellness issues!
10. Get her involved in something outside of school like painting/drawing, photography, sculpting, martial arts, kickboxing, archery, basically any sport or any external creative outlet that is separate from school and separate from her pro-trans peers.
11. Help her to develop her own real identity, not the "identity" of the boy she thinks she might be inside. Often the boy inside is just a coping mechanism, but that's all that it is.
In closing, this trend is going to have a devastating impact on today's youth about 10 years down the road. These things are not very well studied, and we are/were their guinea pigs. Be a role model, be a mentor, but most of all, don't be afraid to be a parent. Don't allow yourself to be bullied into this. This is your child's health that is being played with, and your child's health is not a game - it is life or death.
EDIT (7/26/14): Portuguese translation: http://sexoimporta.tumblr.com/post/91519992159/conselho-para-pais-de-meninas-adolescentes-e-meninas