This is what the Criminal Code of Canada has to say about "written material':
163.1 (1) In this section, “child pornography” means
(a) a photographic, film, video or other visual representation, whether or not it was made by electronic or mechanical means,
(i) that shows a person who is or is depicted as being under the age of eighteen years and is engaged in or is depicted as engaged in explicit sexual activity, or
(ii) the dominant characteristic of which is the depiction, for a sexual purpose, of a sexual organ or the anal region of a person under the age of eighteen years;
(b) any written material, visual representation or audio recording that advocates or counsels sexual activity with a person under the age of eighteen years that would be an offence under this Act;
(c) any written material whose dominant characteristic is the description, for a sexual purpose, of sexual activity with a person under the age of eighteen years that would be an offence under this Act; or
(d) any audio recording that has as its dominant characteristic the description, presentation or representation, for a sexual purpose, of sexual activity with a person under the age of eighteen years that would be an offence under this Act.
Canlii refers to some commentaries:
Written materials must provide some "active inducements" or "encouragement" of sexual activity with persons under 18 years.
This may be be implicit from the narrative of the stories themselves.
R v Beattie (2005) (ONCA):
"[14] None of the 33 stories explicitly counsel or advocate committing sexual offences with children. Overall, however, these stories send two explicit and clear messages to the objective reader of them. First, they send the message that children want and enjoy sex with adults. Children encourage sex with adults -- even their fathers -- by becoming precocious, flirtatious, even manipulative. They are sexually insatiable and ready for repeated sexual encounters. And they enjoy sexual activity even when it is painful and violent.
[15] Second, these stories send the message that although society seemingly disapproves of sex between adults and children, those adults who love children the most and understand them the best (their parents) and those adults who are responsible for their well-being (their parents and doctors) routinely have sex with children. According to the stories, adults do so because they appreciate that children not only enjoy but benefit from sexual activity."