Chemical exposure during pregnancy may also be a factor that causes language delays. Environmental factors
Interactive communication and parental inputs
Psychosocial deprivation can cause language delays in children. An example of this is when a child does not spend enough time communicating with adults through ways such as babbling and joint attention. Research on early brain development shows that babies and toddlers have a critical need for direct interactions with parents and other significant care givers for healthy brain growth and the development of appropriate social, emotional, and cognitive skills.A study examining the role of interactive communication between parents and children has shown that parents language towards toddlers with language delay differ from parents language towards typically developing toddlers in terms of the quality of interaction. While late talkers and children with typical language development both receive similar quantitative parental input in terms of the number of utterances and words, parents of late talkers are found to respond less often to their children than parents of children with typical language development. Parents of late talkers tend to change or introduce topics more often than other parents in order to engage their children in more talk rather than responding to their childs speech. They also seem to not provide an environment that is suitable for child engagement, nor do they establish routines that serve as a platform for communicative acts with their children. This, together with the fact that they respond less often to their children, shows that parents of late talkers do not follow their childs lead.
They may also have troubles communicating non-verbally by using hand gestures, eye contact and facial expressions. The extent of their language usage is heavily influenced by their intellectual and social developments. The range of their skills can be very different and on opposite ends of a spectrum. Many children with autism develop some speech and language skills, but not like typically developing children, and with uneven progress.Asperger syndrome, which is classified under the broad umbrella term of autistic spectrum disorder, however, is not associated with language delay. Children diagnosed with Asperger syndrome have decent language skills but use language in different ways from others. They may not be able to understand the use of language devices, such as irony and humor, or conversation reciprocity between involved parties.Heritability
Genes have a very big influence in the presence of language impairments. Neurobiological and genetic mechanisms have a strong influence on late language emergence. A child with a family history of language impairments is more likely to have delayed language emergence and persistent language impairments. They are also 2 times more likely to be late talkers as compared to those with no such family history.Genetic abnormalities may also be a cause of language delays. In 2005, researchers found a connection between expressive language delay and a genetic abnormality: a duplicate set of the same genes that are missing in individuals with Williams-Beuren syndrome. Also so called XYY syndrome can often cause speech delay.Twins

Being a twin increases the chance of speech and language delays.