A literal translation of the title would substitute "watermelon" for "pumpkin"; however, the phrase has pop culture cachet from being an intentional mistranslation of "The Great Pumpkin" from the comic strip, Peanuts.
Plot
Valentina, nicknamed Pippi, is the daughter of two rich spouses. After having had an attack of epilepsy she is admitted to the department of child neuropsychiatry. The doctor who takes care of her is Arturo, who is immediately convinced that the child has these attacks due to psychological and not psychiatric problems and her family is involved.