There are two types. Dragons from western mythology. And the dragons from Chinese mythology. There are more of the former than the latter. Both can transform into a human-like form.
In the case of the Dragons that are based from western mythology. You find out that dragonnewts like Castor and Carla, are descendants of a dragon and a human. When a male human and a female dragon bear children. The child will either be one of three races: a human, a dragonnewt(human dragon hybrid), or a dragon. There is also a rule that if it is a dragon, it is usually taken back to be raised by other dragons instead of the parents.
Also, the dragon’s chosen partner’s gender causes the dragon to change. Like if the partner is a human woman for example, and the dragon is also female. The female dragon will gender change to male. This also changes what children they can bear as the result will only be human or dragonnewt. Since a human mother can’t give birth to a dragon child.