For Secular Schools in the Netherlands

Education in the Netherlands has strong relations with organized religion, with a multitude of Protestant, Catholic, Evangelical and to a lesser extent Islamic and Jewish schools.
Already in the 1930's the government started campaigning for [secular] public schools, under the slogan "Onverdeeld naar de openbare school" ("Undivided to the Public School"). 

In a predominantly white country, in the 1940s and 50s, the diversity of the children shown on this poster and matchbox is rather small - a beret (typical headgear for children then) could create some diversity.