Deborah Stevenson wrote about the Canon of Significance vs the Canon of Sentiment. "Academic canon exists to fill a variety of needs, both artistic and professional; scholars are likely to discuss books about which they have something to say" (2). The canon of significance is where the literature is designated if it is analyzed, studied and written about by academic critics. The Canon of Sentiment "exists to preserve-- to preserve the childhood of those adults who create the canon and to preserve the affection those adults feel for the books within it" (2).
From what I have learned from Mrs Frisby and the Rats of NIMH, I think it straddles both the canon of Significance and the canon of Sentiment. It is significant because scholars have looked to the novel to find meaning. There is even a chapter dedicated to the novel in a book called Philosophy in Children's Literature. It is a book that evokes thoughts about Utopia, Goodness and Intelligence.
But in addition to the thought-power that has been inspired by Mrs Frisby and the Rats of NIMH, there is also a beloved tale. It is a pretty traditional tale with regards to the plot. Mrs Frisby has trouble, she makes friends who help her and her home and family are safe and sound. The story was so loved by children (and adults) that the author's daughter wrote two sequels and there was a movie made (as well as a sequel to the movie!). According to deadline.com, there is a CGI movie currently in the works. It has been over 40 years since the novel was first written and it continues to inspire more works and young minds.