The recent surge of interest in this area may be due to the recognition that being monolingual is not the common state. Romaine (1989) explains this saying that there are “thirty times more languages ​​than there are countries... This implies the presence of bilingualism in practically all countries in the world” (p.8). Bilinguals can be elites who have chosen to be bilingual, or popular bilinguals, forced into a situation where the acquisition of another language has become a necessity. Genesee defines bilingual acquisition as “the acquisition of two languages ​​during the period of primary language development, extending from birth” (2000, p. 167). Acquiring two languages ​​can be done one language at a time (sequential) or at the same time (simultaneous). This article will focus on simultaneous bilingualism, otherwise known as bilingual first language acquisition: the valid or three-stage model. Bilingual First Language Acquisition Ng and Wigglesworth (2007) give a broad definition of bilingual first language acquisition (BFLA) stating that it is “the learning of two languages ​​in a naturalistic setting, in which be acquired both the formal aspects and the social conventions of languages. Thus, the child must learn the phonological properties of both languages” (p.40). Most research agrees that it is from birth until the age of three. However, it can be said that at three years old the child already begins to speak fluently. The first spoken word extends from the age of ten months to fourteen years. Keeping in mind that a child accumulates language even before speaking, it is possible to reduce the age limit; The critical period hypothesis gives a parallel estimate. “The researchers made a distinction between two c...... middle of paper ......e German-English bilinguals. GRIN Verlag. Leopold, W. F. (1947). Speech development of a bilingual child, file from a linguist...: grammar and general problems during the first two years. III. Northwestern University Press. Meisel, J.M. (2011). Acquisition of a first and second language: parallels and differences. Cambridge University Press. Mey, J.L. (2009). Consise Encyclopedia of Pragmatics. Ng, B.C. and Wigglesworth, G. (2007). Bilingualism: an advanced resource book. Taylor and Francis. Romaine, S. (1989). Bilingualism. B.Blackwell. VanPatten, B. and Benati, AG (2010). Key terms in second language acquisition. Continuum. Volterra, V. and Taeschner, T. (1978). The acquisition and development of language by bilingual children. Journal of Children's Language, 5(2), 311-326. Yule, W. and Rutter, M. (Eds.). (1987). Language development and disorders. Cambridge University Press.