I'm not sure who specifically 'Carlton from True Story' is without more context. There could be many people named Carlton in various true stories. It might be a character from a local event, a family's true story, or perhaps a story within a particular community.
One popular 'ross and demelza fanfiction' story could be about their life after the series ends, showing how they deal with new challenges in Cornwall. Another might focus on a what - if scenario, like if they had met under different circumstances. There are also fanfictions that explore their relationship in more depth during the time gaps in the original story.
In the fanfiction, it might be that there was a special event. For example, a big gathering where people from different places came together. One of the guests had the flu but didn't know it. Demelza interacted with this person, like sharing a drink or just being in close proximity for a long time, and as a result, she got the flu.
It could lead to her being bedridden for a while. And this might make other characters worry about her. For example, Poldark himself would be very concerned and might neglect some of his own affairs to take care of her.
Since I don't have more information about this 'Carlton True Story', it could cover a wide range of things. It could be a story of Carlton's personal growth, like how he overcame challenges in his career or in his family life. Maybe it's about his adventures in a particular place or his contribution to a certain community. It could also be related to some historical events that Carlton was involved in, but again, without more context, it's just speculation.
There are so many possible 'kid and carlton true story' scenarios. It might be a local story in a particular community, or it could be a story within a family. If you can provide some context like where the story is from, what kind of relationship the kid and Carlton have (e.g. brothers, friends), or what the general theme of the story is (like a rescue story, a coming - of - age story), it would be much easier to answer.