Studies (Petitto) show that the stages of language acquisition from birth to age 5 and beyond are identical among infants in both signlan and speech.
Furthermore, study (Petitto and Marentette) found that bilingual-bimodal hearing infants exposed to signed and spoken languages do babbling in both manual and vocal within the same developmental stages of language.
"Acquisition of Sign Language Challenges Linguistic Theory." (slides) VL2, Gallaudet University. October 11, 2007.
Paula F. Marentette. "Babbling in Sign Language: Implications for Maturational Processes of Language in the Developing Brain." 1989.
Anne Baker, Benice Woll. Sign language acquisition. pp 41-?
Karen Emmorey (2002). "Sign Language Acquisition." Language, Cognition, and the Brain: Insights from Sign Language Research. Chapter 5, pp 169-204.
Gary Morgan. "Directions in sign language acquisition."
Laura Ann Pettito and Paula F. Marentette. "Babbling in the Manual Mode: Evidence for the Ontogeny of Language."
Laura Ann Petitto. "Bilingual signed and spoken language acquisition from birth: implications for the mechanisms underlying early bilingual language acquisition".
"Language rhythms in baby hand movements".
Marc Marschark, et al. "The Development of American Sign Language and Manually Coded English Systems." The Oxford Handbook of Deaf Studies, Language, and Education, Volume 1. Chapter 16, pp 229-240.
Wataru Takei. "How Do Deaf Infants Attain First Signs?" Developmental Science, 4: 71-78.
Mounty, Judith Lynn. "Nativization and Input in the Language Development of Two Deaf Children of Hearing Parents" 1986. http://www.eric.ed.gov/PDFS/ED334723.pdf