Bilingualism, as the topic of this thesis, is increasingly being researched and supported within the framework of recent pedagogical science precisely because of the cognitive and social advantages it provides to the child. Modern approaches to education seek to integrate bilingual programs into the system of regular classes and thereby facilitate learning outcomes for bilingual students, but also support their linguistic and cultural diversity. In practice, bilingual programs offer a number of models and forms of bilingual education that are individually shaped according to the linguistic and cultural needs of students with the aim of achieving absolute bilingual competence in both languages. When raising and educating a bilingual child, the competencies of the parents themselves, and then of the educators, professional associates and teachers, as well as the involvement and interest of the educational institutions are extremely important. The conducted research will deal with the case of a bilingual preschool child who has been exposed to two languages in his household since birth, and the method of language acquisition called "one parent-one language" will be presented. Although the mentioned method belongs to one of the most well-known approaches in raising bilingual children, it can only succeed if the parents, family and the child's environment are persistent in it.