If you are looking for adult Sinhala content with some quality, note that genuine (e.g., by authors like Piyasena Kahandagamage in his more daring works, or modern online writers) differ greatly from "Wala Katha":
: Reliable for finding historical documents and public domain Sinhala literature. Sinhala Wala Katha Full
Why should a parent or teacher search for rather than a summarized version? If you are looking for adult Sinhala content