Part of the "Stolpersteine" (stumbling blocks) project, set up by the German artist Gunter Demnig, who commemorates the victims of the Nazis. The ccovers are usually placed in front of the houses of the victims.
Westerbork transit camp - one of the two transit camps set up for Dutch Jews before their deportation to the camps.
This seems to be a couple of parents and their two children, with the father separated from the mother and the two children.
Translation of the text on the cover: Here Lived Louis Bremer Born 1919 Deported 1943 Via Westerbork Murdered 17.2.1945 Dachau
Here Lived Esther Bremer Sanders Born 1919 Deported 1921 Via Westerbork Murdered 10.9.1943 Auschwitz
Here Lived Joseph Bremer Born 1940 Deported 1943 Via Westerbork Murdered 10.9.1943 Auschwitz
Here Lived Benedict Bremer Born 1943 Deported 1943 Via Westerbork Murdered 10.9.1943 Auschwitz