Okay, so back to thinking about desaparecidos en literatura para jovenes. Another book that touches on the theme is Los desmaravilladores (10 cuentos de amor, humor y terror), by Elsa Bornemann. The final story (Los desmaravilladores, from which the book takes its name) addresses the problem of discovering that your adoptive parents have (in this case unwittingly) adopted you after your biological parents were disappeared.
The story is framed as a short story being submitted under a pseudonym to a historical story competition run by the Academia Nacional de Historia de la Republica de Sudaquia. This short story itself is framed by the book of short stories in which it is published and to which it gives its title. This frame seems full of meta-narrative! But the story itself is fairly straight forward.
(Question: Is setting this story in the Republic of Sudaquia like re-claiming an insult – like has been done more classically with the terms nigger or gay? There is a publishing house by the same name: http://sudaquia.net/ and a blog http://weblogs.clarin.com/sudaquia/ but this is new to me and as far as I can tell it comes from an insult that has been reclaimed (http://en.wikipedia.org/wiki/Spanish_profanity#Racial_and_ethnic_derogatives) …I don’t know!)
NB One site describes the book: “Un libro de cuentos que habla de los primeros encuentros con el terror. Cuentos que además recrean leyendas populares o acontecimientos reales, con la valentía de quien sabe que para los chicos no existen temas difíciles. Sólo se trata de saber contarlos.” http://www.librosalfaguarainfantil.com/ar/libro/los-desmaravilladores-1/