In this chapter, from the perspective of child psychiatry, the authors discuss the urgent need for contemporary multicultural societies to reassess their attitudes to language. This will enable children from multilingual families to learn the second Mother tongue that is crucial to their assimilation. This chapter focuses on the children of migrant families who are afflicted by an ‘aporia of transmission’, leading to premature school leaving and in some cases separatism. Although French-language policies have remained broadly monolingual, the authors have followed in the footsteps of Georges Devereux, the founder of ethnopsychiatry, and his disciple, Tobie Nathan, to open up child psychiatry to a transcultural approach. Placing the Mother tongue at the centre of the therapeutic protocol at the Maison de Solenn, a new discipline called ‘parent–child ethnopsychology’ has been established, its clinical success bringing new arguments to the controversy surrounding the monolingual language policy prevalent in French schools. The authors offer a clinical perspective on the problems some children and adolescents face, deprived of their heritage or torn by a conflict of loyalty between disparate languages and values, forced to negotiate two modes of belonging: filiation and affiliation.