The Hashiras would likely show concern. Some, like Shinobu, would immediately start looking into possible medical solutions. Giyuu might be more reserved in his worry but would still keep a close eye on Tanjiro. The other demon slayers would also be affected. They look up to Tanjiro, so his sickness would lower the morale of the group. They would try to support each other while waiting for Tanjiro to recover.
Some adults may feel extremely humiliated. They are no longer children and being spanked makes them feel as if their parents don't respect their adulthood. For example, they might become withdrawn and avoid family interactions for a while.
Tanjiro might use his sense of smell to detect hidden threats. Since his sense of smell is super - enhanced, he could sniff out any demons or traps in the way of saving Rengoku. For example, if there are demons disguised as allies, Tanjiro would be able to tell by their scent.
First of all, communication is key. If a parent catches something like a gay nanny teaching their child about acceptance of all sexual orientations, they should sit down and have a conversation with the nanny. They need to set boundaries if necessary, but also appreciate the positive aspects such as promoting inclusivity. For example, if the nanny is just showing the child that there are different kinds of families in the world through stories, it can be a good thing as long as it is age - appropriate.
If parents come across disturbing content in Descendants fanfiction, they should immediately stop watching it. They can also report the content to the platform where they found it if possible.
Parents can react with understanding. They should create an open environment where the teen feels comfortable to talk. For example, instead of getting angry immediately, they can listen to the teen's feelings and experiences.