In December 2015, the heirs of Edith Newlin filed a lawsuit against the various companies associated with The Big Bang Theory, claiming that the words and music to the song appeared in the book Songs for the Nursery School published in 1937 by Willis Music, based on a poem by Newlin; the copyright to the book was renewed in 1964. The website for Willis Music states:
In 1937 we published a book called Songs for the Nursery School and we sold tens of thousands of copies. It is a hardbound book of over 150 songs for children. The book was written by Laura Pendleton MacCarteney. In that book on page 27 is 'Warm Kitty'... Warner Brothers and I worked together to secure the rights for the show The Big Bang Theory and they have been using the song ever since.
The suit by Newlin's daughters, on the other hand, claimed that they held the copyright. Furthermore, they alleged that they did not authorize the use of the lyrics, that Willis Music did not have permission to authorize others to use the lyrics, and that the lyrics had been used not only in the television series but on various kinds of program-associated merchandise without proper permission.
On March 27, 2017, US District Court Judge Naomi Reice Buchwald dismissed the suit, holding that the plaintiffs had not shown that they held copyright on their mother's lyrics. Applying section 24 of the Copyright Act of 1909, a provision that Buchwald characterized as "hardly a model of clarity", the court found that Willis Music's renewal in 1964 of its registration for Songs for the Nursery School did not also renew Newlin's copyright for "Warm Kitty".