Wanting to be transgender

Before You Begin
Pause and breathe. Even if this shouldn't be happening... accept that it is and embrace it with composure and calmness.
Calmness is the only way forward because without calm, there is no possibility for receptiveness and connection. Your child won't give to you any more than they see from you.
Never forget that a strong connection is fundamental, as there will be no correction in them if there is no connection with you.
The Core Problem
Depending on your beliefs, this may or may not be a problem but it is certainly an important time in their life that needs to be handled well.
This is a rare circumstance where "a successful outcome" is more dependent on the parent's ability to have unwavering empathy, connection with, and love for their child throughout the conversations on this topic.
What Will Make It Worse
Ignoring your child's attempts to discuss this side of themselves or having a negative response won't change how they feel, it will only deteriorate your relationship with them and make their journey more troubling.
What The Child Needs
1. To think deeply about what is happening in their life that being transgender is the solution: It is critical that they are able to explain what problem in their life will be completely and forever solved by changing their gender. If they cannot identify what their driving reason is, or if there is a disconnect between the problem and a gender change being the solution, help them to see that this likely isn't a good thing to proceed with.
2. To identify what new problems/challenges/hardships they are inevitably going to bring upon themselves by becoming transgender: Any major change in your life, from moving to another city to starting a new job, will introduce its own set of new challenges. Have them honestly imagine what scenarios they will face as a direct result of this decision, and if those will be worse than what they are dealing with at the moment.
3. To know that this is not something they will have to navigate alone: Connection with your child during this time is incredibly important. They will appreciate having an adult to guide them around the hidden dangers that they know they likely can't see for themselves. In taking this journey with them, you and they will know how you got there and that it will not affect your relationship.
4. To educate themselves and you on what the process is to be transgender: This is not something most people, let alone kids, have a thorough knowledge of. Help them seek out unbiased, credible, professional and medical resources so that both you and your child can erase any uncertainty or confusion about how to transition.
5. To acknowledge the irreversible consequences of being transgender: Do not let your child underestimate the forever impact this will have on their body. There is no other possible thing they could do to more permanently change themselves. Get them to see how things like tattoos, hairstyles and piercings may seem extreme yet they are incredibly minor compared to being transgender.
6. To hear stories from both sides of those that made the transition: A person's story can be incredibly moving and persuasive. Have them find those who have made the transition who were happy they did it and also those who severely regret the decision. Hearing firsthand from both sides will help them to make a confident decision about whether to proceed.
How To Have The Conversation With Your Child
Find a time where you and the child are relaxed and can talk in an environment that is private, comfortable and distraction free.
Let them know that you very much want to hear what they think about being transgender and all the emotions they are feeling. Use the provided "What The Child Needs" points 1, 2, 3 and 5 as a way to structure the conversation and flow from one important consideration to the next.
Make sure it is a two way conversation, that is taken seriously but still encourages full unguarded honesty and open communication.
[Points 4 and 6 will need to happen over time as they require seeking out information]
Regardless which point you are guiding the child through/discussing, it is above all important to have the child feel like you want to go on this journey alongside them and they can count on your support and more developed ability to think through things.
This is likely the most difficult decision of their life, and one that they don't want to do alone.