From birth, babies can distinguish all sounds from all the languages in the world - more than 800 different phonemes! However, this initial universal ability to distinguish between sounds of different languages gradually decreases between the ages of 6 to 12 months. Kuhl, P. K. (2004). Early language acquisition: Cracking the speech code. Nature Reviews Neuroscience, 5(11), 831-841.
Research shows that in babies from dual-language homes, brain processing activity is specialized to process the sounds of both languages by 11 months of age. Ferjan Ramírez, N., Ramírez, R.R., Clarke, M., Taulu, S. and Kuhl, P.K. (2017), Speech discrimination in 11-month-old bilingual and monolingual infants: a magnetoencephalography study. Dev Sci, 20: e12427.
Babies who are read to regularly have a 40 percent increase in receptive vocabulary by the time they are 18 months old. High PC, LaGasse L, Becker S, Ahlgren I, Gardner A. Literacy promotion in primary care pediatrics: can we make a difference? Pediatrics. 2000 Apr;105(4 Pt 2):927-34.