Children often start the transition process on their own by changing the way they present themselves. They may want to dress or wear their hair like the gender they identify with, maybe just at home at first. At some point, they may want you to call them by a different name and use different pronouns. With the right support, kids can work up to living full-time in the gender they identify with. These are all completely reversible steps, and they may be all that your child needs to feel comfortable.
