By: Virginia Li, Danielle Dietz, CCC-SLP and Ashley Springer, CCC-SLP –  Pathways.org
Bilingualism provides children with a number of long-lasting cognitive, emotional, and cultural advantages. The term bilingualism will be defined here as an individual’s ability to use two or more languages.
By understanding the process of language development in young bilingual children, speech-language pathologists and other child care professionals can better recognize the difference between typical and atypical development, and address the needs of bilingual children and their families.
Typical Bilingual Development
Bilingual children typically acquire their languages in one of two ways: simultaneously or sequentially. Simultaneous acquisition occurs when a child is introduced to multiple languages from birth or before the age of 3. Young simultaneous language learners will experience the same developmental trajectories as monolingual children, and are able to differentiate between their languages early on [1].
Sequential acquisition is when a second language is introduced after the native language is established. This may happen after immigration, or if a child speaks a minority language at home until starting school in the community’s majority language. After initial exposure to the new language, sequential learners may experience a “silent” period during which they focus on language comprehension rather than production. When they do begin to speak, they’ll make mistakes similar to those of monolingual learners of that language, and may mix in elements of their home language.
Language proficiency among young bilingual children is quite varied, as additional factors including age, exposure, motivation, and even personality contribute to the rate and balance of language development [2]. Children may learn one language better than the other, and the stronger language can change over time. Those who limit communication in their first language while learning the second can experience language loss, or subtractive bilingualism. This may cause them to go through a developmental phase in which their home language abilities decline before they have gained age-appropriate proficiency in their second language. Clinicians must take these factors and developmental processes into account when performing language assessments in this population.
Common Misconceptions
Parents raising children in a bilingual household are often confronted with a number of negative misconceptions regarding early bilingual development. Four common myths are highlighted below.
Myth #1: Bilingualism leads to language delays. 
This is a common concern among parents raising bilingual children. However, there is no evidence that learning more than one language at an early age causes delays in language development [3]. Bilingual children will reach major language milestones at the same pace as their monolingual peers, with first words appearing around 11 to 14 months.
Myth #2: Code-switching (language mixing) is a sign of confusion.
Code-switching, defined as the act of alternating between languages in a single conversation, is a natural part of dual language learning. While parents may worry that code-switching indicates confusion, it is actually a sign of a child’s proficiency in each language. Research shows that young bilingual children consistently speak the language their listener knows best, thereby demonstrating sensitivity to their sociolinguistic environments [4].
Myth #3: Speaking the home language will interfere with a child’s acquisition of the majority language.
To build their communication skills, children need exposure to a rich language model during early development, and parents should be encouraged to speak to their children in the language that they are most comfortable with. A strong foundation in their first language will help children acquire a second language.
In the United States, some parents believe that their children will gain greater proficiency in English if they only learn English, leading them to limit their children’s interactions in the home language. For children who rely on multiple languages for meaningful daily interactions, regressing to one language can have negative consequences, such as social isolation from family members who only speak the home language [5].
Myth #4: Children with language or learning impairments should not learn more than one language. 
Recent research has shown that children with specific language impairment (SLI) [6], Down syndrome [7], and Autism Spectrum Disorder (ASD) [8] are able to learn more than one language simultaneously without experiencing additional delays or challenges compared to monolingual peers with similar impairments. Additional research is needed to understand the process of sequential bilingual development in children with language and learning impairments.
Bilingualism in young children is a gift that should be supported rather than suppressed. Child care professionals, including speech-language pathologists, health care providers, and teachers, can be instrumental in exposing these outdated myths and reshaping general attitudes about early bilingualism.
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References:
[1] Genesee, F., Nicoladis, E., Paradis, J. (1995). Language differentiation in early bilingual development. Journal of Child Language. 22:611-631.
[2] Tabors, P. 1997. One child, two languages. A guide for preschool educators of children learning English as a second language. Baltimore, MD: Paul. H. Brookes Publishing Co.
[3] Petitto, L.A., Holowka, S. (2002). Evaluating attributions of delay and confusion in young bilinguals: Special insights from infants acquiring a signed and spoken language. Sign Language Studies, 3(1):4-33.
[4] Genishi, C.S. (1976). Rules for Code-Switching in Young Spanish-English Speakers: An Exploratory Study of Language Socialization [Doctoral dissertation].Retrieved from ERIC.
[5] Wong Filmore, L. (1991). When learning a second language means losing the first. Early Childhood Research Quarterly, 6:323-347
[6] Paradis, J., Crago, M., Genesee, F. & Rice, M. (2003). Bilingual children with specific language impairment: How do they compare with their monolingual peers? Journal of Speech, Language, and Hearing Research. 46:1-15.
[7] Kay-Raining Bird, E., Cleave, P., Trudeau, N., Thordardottir, E., Sutton, A. & Thorpe, A. (2005). The language abilities of bilingual children with Down Syndrome. American Journal of Speech-Language pathology. 14:187-199.
[8] Peterson, J. Marinova-Todd, S.H., Mirenda, P. (2012). Brief report: An exploratory study of lexical skills in bilingual children with autism spectrum disorder. Journal of Autism and Developmental Disorders. 42:1499-1503.