So far polish studies have look at the linguistic capacity of deaf children at their apparent linguistic deficiencies when compared to some idealized standard of Polish. The Polish Sign Language turns out to be the real language, which has rich vocabulary, and complex grammar and can convey the same subtleties and complex meaning that spoken language can (Farris, 1994; Tomaszewski, Rosik, 2002). Furthermore, deaf child of deaf parents can acquire this language spontaneously from the natural linguistic environment. The goal of this paper is to answer for fundamental questions: how does language modality affect the nature of the language acquisition process? Do the properties of sign language affect the course and timing of language acquisition? This paper traces the acquisition of sing language by deaf children of deaf parents from manual babbling and communicative and linguistic gestures in infancy, to the acquisition of morphology and syntax early childhood. Analysis of the role of sing language in development could provide important insight into the nature of human language and the human process of communication.