Stephen Fry (Sir Simon de Canterville) previously played Oscar Wilde, the author of the short story on which the film is based, in Wilde (1997).
Sir Simon de Canterville quotes from three Shakespeare plays - Hamlet, Macbeth and Twelfth Night (the song he's singing when Virginia breaks into his prison)
In the original text the Otis have four children; Virginia, her younger twin brothers Stars and Stripes (Louis and Kent) and her older brother Washington. In many adaptions Virginia is the only Otis child to be featured as her brothers are written out. In this version although Virginia's twin brothers are featured her older brother is left out.
Freddie Highmore, Hugh Laurie and Stephen Fry all they played doctors respectively in TV series: Highmore played Dr. Shaun Murphy in The Good Doctor (2017), Laurie played Dr. Gregory House in House (2004) and Fry played Dr. Gordon Wyatt in Bones (2005).