Perhaps to underscore the different treatment afforded minors, in Spain the terminology of juvenile justice (justicia penal de menores) is quite different from the terminology used to describe the criminal prosecution of adults. In that regard, in adult felony proceedings (proceso penal ordinario) the preliminary investigation is known as a sumario, while in juvenile justice the equivalent is expediente de reforma. Thus bringing a criminal action against an adult is expressed as incoar un proceso penal, while in juvenile procedure this is called incoar un expediente de reforma. The questioning of an adult suspect may be described as interrogatorio del investigado (formerly, imputado) and is conducted by an investigating judge (juez instructor). In juvenile justice terms the interrogation of a minor is known as exploración del menor and is carried out by a prosecutor (fiscal).
Pretrial detention, known as prisión provisional or prisión preventiva in adult contexts, is internamiento cautelar when it involves a juvenile. In certain circumstances an adult may for a limited period be placed in isolation or solitary confinement, known as prisión provisional incomunicada; but this is called internamiento incomunicado if imposed on a minor. And rather than juicio oral, the trial of a minor is referred to as an audiencia.
Criminal sentences, known as penas when imposed on an adult convicted offender, are called medidas when imposed on a minor. Thus, enforcement of a criminal sentence is ejecución de la pena in adult contexts, but is known as ejecución de la medida when applied to juveniles. A custodial sentence for adults, pena privativa de libertad or, more specifically, pena de prisión is called medida de internamiento when applied to juvenile offenders, who are known as menores infractores.
Convicted adults may be sentenced to incarceration in a centro penitenciario, while juveniles serve custodial sentences in a centro de internamiento (de menores) and are known as a menores internados rather than as internos or reclusos, as adult prisoners are called. In addition to these and other differences in terminology, it should perhaps be noted that the rules of procedure for trying minors set forth in Ley Orgánica 5/2000, de 12 de enero, reguladora de la responsabilidad penal de menores (and subsequent amendments) are radically different from those governing the prosecution of adults under the Ley de Enjuiciamiento Criminal. And cases against minors are always heard in a juvenile court (juzgado de menores) by a specialized juvenile court judge (juez de menores).
For further reading:
José Luis de la Cuesta and Isidoro Blanco. “El enjuiciamiento de menores y jóvenes infractores en España.” Electronic Review of the International Association of Penal Law (Revista Electrónica de la Asociación Internacional de Derecho Penal) A-03, 2006.