Maria Klejdysz

In Nazi occupied Poland, a young priest is approached by a Polish resistance fighter who has been given orders to execute a local man accused of treason. The resistance fighter is seeking absolution and forgiveness, in advance, for killing the local man. The young priest is hesitant to grant such a request... (summary by BadCosmonaut)

As a result of a mistake, the siblings change roles and go on vacation somewhere else than planned. The boy goes to his aunt and cousins, the girl goes to her uncle and cousins. To save her brother, the sister pretends to be a boy and he, left with no choice, pretends to be a girl.