Fair Use is a special blessing for education, art, commentary, review, parody, etc. Recent NYT review for the Dr. Seuss inspired “Who’s Holiday!” work following the life of Cindy Lou Who, who then was not much older than two. She growed up (https://www.nytimes.com/2017/12/04/theater/review-whos-holiday-dr-seuss.html).
Matthew Lombardo was sued, by the Grinch, Dr. Seuss Enterprises, for stealing and with good reason as derivative works are very well protected, particularly for works of fiction (ask JK Rowling!). But the courts did see a fair use exception and Matthew Lombardo won the case and for a fairly new reason – the work was considered transformative! Interesting reading on other issues of copyright related to this case and apparent inconsistencies in determining whether fair use should/should not apply – https://www.nytimes.com/2017/09/15/books/dr-seuss-grinch-law-suit.html