There already exists a feature suggestion for a profanity filter (e.g. based on scanning subtitles).
As for blocking individual scenes… are you sure you want to expose your kids to a hard-core porn or bloody horror film… just blurring/skipping the bad scenes?!
Plex has a number of parental controls. Mainly focusing on kids with their own managed account (as explained by crhatfield). Those target to define what movies your kid can see – not to filter individual scenes.
One example is to manually label movies you want your kid to be able to see (and then having a managed user that’s only allowed to see movies tagged that way).
Alternatively you can assign a “restriction profile” to such an account that restricts the account to movies approved for certain age groups (available profiles are small kid, kid, teen and no-restrictions).
https://support.plex.tv/articles/parental-controls/
