Make your home an inclusive one. No, this doesn't mean leaving your doors unlocked, I'm far too paranoid an American to recommend that. But one of my biggest disadvantages growing up (which was in no way my own folks' fault, as transpeople still aren't common knowledge now) was not knowing that transgender people existed. It's easily segued from the love conversation: sometimes girls love boys, sometimes girls love girls, and sometimes girls want to be boys. Even when I was very young, I latched onto any examples of gender variance in my life, and when they were negative images (like from porn), I didn't have any parentally-backed ones to counterpoint them with. Set a good example by making it seem normal, boring and everyday.
Don't equate "Mommy I want to wear girls clothes" with "Mommy is the stork going to make a second trip to drop off my vagina?" Just because your child has these feelings doesn't mean they are trans, genderqueer or simply fabulous. However, they do need the space to figure themselves out, and if you deny them that I guarantee you the feelings will only intensify over time. If you deny them this chance to express themselves in a way that doesn't hurt anyone, it will only lead to complexes, trust issues and even more identity issues. SPOILER ALERT: everything you do as a parent makes these.
Talk to your kid about how far they want to go right now. Some are aching to change everything now, some are just wanting to test the waters in a safe space. Talking takes precedence, and that's why this is an okay time to exert some parental authority and say "You can't have everything now." But girls tend to like piercings, and boys like shorter hair, so why not start there?
Consider a therapist, but only if you're willing to do some leg work. Therapists need to be asked about their familiarity with gender, and working with kids. Also, seek out trans or LGBT support groups and ask if they have any therapists to recommend, or advice to offer. If you have a middle school or younger age kid, consider going without them to that meeting the first time (you need to make sure this is a good group, because not all are). However, if your child tends towards the hyper confident end of the spectrum and doesn't mind outing themselves to a group of strangers, you go, transkid.
Don't run and tell everyone that your kid is trans just to get it over with. Tell people as they need to know, unless there's a family member or friend your kid feels they should tell, and is one that you feel will react in a positive manner. If you're Super Parent (and if you are, sorry about everyone on Krypton dying and everything, that sure sucks), you may want to go telling your family and friends The New World Order, but the more people who know the more pressure can be put on a child to make up their mind one way or another. Also, odds are your kid won't want pronouns out of the gate, so call them your daughter if that's who they are right now, and if they change that to son later, say that later. You're not here to make other people feel comfortable, you're here to make just one person the most comfortable person ever. So do that.
When it comes to schools, talk to their teacher first when they start living a significant period of the day in their new gender's clothing (if they're in elementary school). If there's bullying, talk to an administrator, but don't do so with the assumption you're going to have to fight them all the way to the Lifetime movie adaptation of your struggle. Most people, yourself included until your kid became trans, don't know as much about gender variance, so be ready to take the lead, educate, and make it clear that the school's job is to prevent any kind of bullying. Also, never let changing schools be off the table. If they're in middle school or high school, don't divulge to their, what, eight teachers, until they're going to school in dress. Talk to teachers of whatever classroom they're being bullied in, first, if they're not full time new gender at school.
If your kid changes dress in the younger age bracket (0-10), their peers'll likely just accept what you tell them. "Your girl is a boy? Capital! Now where's your most edible ground?" -Their peers. Really, kids are mega-accepting and submissive to authority figures when they're young. That is, until the fruit of knowledge begins properly digesting and we all become twats in middle school. A good friend of mine (let's call her Tessa) who's a transwoman, fathered a kid just before she transitioned. She told this daughter, Melisa, when she was about 2 that mommy Tessa used to be a boy, but Tessa wasn't happy being a boy and became a girl. Melisa's response even years later? A perpetual motion machine of love.
Hormones can be a comfort for kids, but never let them be a crutch. If they're younger, tell them that if their body starts making them too much like a girl or a boy, they can stop that if they feel comfortable with it. If older, only if they can come to you knowing everything good and bad these drugs do. It's important that they understand their identity emotionally before they get too fixated on their identity chemically. (Hormones don't fix the self, they just give it different wrapping paper)
On fertility. This may be an awkward convo for a suddenly hormonal 11 year old who wants their body to stop changing them the wrong way. Yes, hormones, especially at that young an age, can *potentially* end their ability to have babies forever. Talk to doctors and see if anything can be frozen. If it can't, you and your kid need to decide if X amount of time without hormones is something they (and not you) can live with until something can be frozen. If not, there are an awful lot of unadopted, love-worthy kids on this planet.
Encouragement. Yes, you may need time to mourn the "death" of the child you'll never have again, but don't put that pain on them. They need you to be strong, they need to think of you when they're afraid, and not the fear. If they know someone can stay by them and be strong, that makes all the difference. For ‘xample, I was very hard on myself at the beginning of transition, but GF never flinched in daily reminding me how strong I was and how wonderful I was for being true to myself, and over time, when I would find myself on the floor, wet eyed, shaking and scared, I would stop replaying my fears and would instead remember her, and her sureness. That's what you want: the magic of repetition.
Family who is not on your side will not be accepted. That is all.
Don't force them into their new gender. You know your kid, even if right now it feels like you don't. You know whether or not your kid is the kind who'd be happy to come home from school one day and find their room pink and every trapping of their old life replaced with bunnies, bunnies and more bunnies. You see, whether I'd been born guy or girl, I'd still think My Fair Lady and Starship Troopers are excellent, so let your kid explore their gender rather than tell them what it is. I wouldn't have been broken hearted to come home and find Ultraman hugging a stuffed kitty.
Part of encouragement is telling them it's okay to be wrong. They need to know they can come to you with doubts, especially if they want to change their minds about hormones, pronouns, their name, anything. Would you want to be judged? No? Then do unto others.
Don't erase yourself from this equation. Have a support network of your own, because you'll need someone to lean on if this hurts. It's not your kid's fault, nor yours, but the biggest trip-up in parenting is pretending you're a magic fixit machine. You're a person who feels. Just spare the child the woe you're writing in your heart and save it for that certain someone great at making you feeling less ARRGH-sad.
Stand up for them. They're very probably terrified in one way or another, and if they don't learn to expect someone to stand up for them, they'll withdraw, hiding their real self in the dark place where it's safe. Correct people on pronouns. Stare back at starers. Answer questions to your heart's content, not someone else's. You can always walk away from a conversation and no one will arrest you. If someone tries to tell you about how to raise your kids, well, if you're in the 1950′s you can say "Sure thing, Mrs. Willoughby, we'll get right on that." If you're in New York you can say "Yourself: go fuck it." Or if you're a regular person you can say something hokey like "I'm just letting my child be who they are in a way that doesn't hurt anyone," because you're a parent and you say things that are well-intentioned and hokey.
If there's trouble at school, keep records of it. Who with, what day. This will give you something to bring to administrators, PTA meetings, teachers, etc.
Make sure you and your kid understand the difference between privacy and secrecy. Secrecy is frequently something you're ashamed of, and that's not what your youngin should feel. Privacy is explaining to your kid that not everyone accepts this, and that telling everyone everything is not what a person does for anything in their life, least of all this. Work out between the two of you what's the right thing to say when asked, like rehearsing a script.
If your child moves back and forth between genders "a lot," accept that maybe they're a crossdresser, maybe they're genderqueer, or maybe, just maybe, they're a person who gets confused and unsure. The same way you do about everything you've ever known, including and especially about who you are. Most of transition is being in a safe space to act out your identity. So it's not about whether your child is "really" a boy or "really" a girl, it's about accepting that your child is your child, and needs help.
Now, post-disclaimer (but ha, you suckers read the whole thing anyway! Except for you down scrollers, who I'll soon exact vengeance upon): this is a guide that was written in reaction to the story of 10 year old Jackie (plus some inspiration from another ABC News piece), but like general parenting 101, there is no 'parenting trans kids 101' textbook. All there is is showing up to class. Situations vary for each kid, regardless of age, but I find that when I'm feeling lost, reading through guides can help shine a light where once there was just darkness to blindly grope about in. You'll make mistakes, but this is how you learn. Or as transman pastor Aaron Raz Link said, "Forgive yourself for learning instead of knowing."