The most recent major study on language learning and age was conducted by researchers at Harvard and MIT. It concluded that starting to learn a new language before age 10 will give a learner the best chance of achieving proficiency similar to that of a native speaker.
They concluded that the ability to learn a new language, at least grammatically, is strongest until the age of 18 after which there is a precipitous decline. To become completely fluent, however, learning should start before the age of 10.
Get Started Early
But by the time a baby is about 10 months old, he begins to narrow down the range of sounds to those that he hears around him. So if you want your child to learn a second language, it's best to introduce it in the first year of life.
So when a three-year-old growing up in a bilingual household inserts Spanish words into his English sentences, conventional wisdom assumes that he is confusing the two languages. Research shows that this is not the case. In fact, early childhood is the best possible time to learn a second language.
Many studies have reported that children can be bilingual right from birth. The much rumoured “window of opportunity” is between infancy and the age five. This is because the brain grows and expands rapidly till the child reaches five years of age. So the more their brain is stretched, the more it develops.
Research overwhelmingly supports teaching second languages early, because as we know it's harder to learn a second language as we get older. But when kids are very young — from birth to about three years old — they are very ripe for receiving new information.
Although it's not typical, your 2-year-old's situation is not necessarily cause for great concern, either. Some more cautious and reserved 2-year-olds tend to wait until they understand a great deal of what they hear before they actually speak.
In conclusion, research has shown that bilingualism does not lead to confusion, nor does it have any inherent negative impact on development. In the early stages of the acquisition of a second language, children hearing two languages can show some developmental lags relative to children who speak only one.
Learning two languages together does NOT cause speech or language delay. Simultaneous learners pick up language skills the same way and at the same pace as monolingual children do. They reach the same speech and language milestones at the same ages.
In contrast, learning a second language too early can lead to a loss of the native language and the inadequate mastery of native language makes it more difficult to learn a foreign language. Academic burden and external factor such as the lack of proper education can hinder the second- language-process as well.
The rule of thumb is that about 30% of a child's waking hours needs to be spent in a language to obtain conversational fluency, so, realistically, you're looking at a max of three languages. Once you have those three languages at a decent level, it would make sense to add another one.
Some people may mistakenly believe that raising a child in a bilingual household (meaning they speak more than one language) puts them at risk for language delays or a “silent period” when they might not speak at all. Language delays can still occur in bilingual children, but bilingualism itself is not the cause.
There are some people who believe that when a child is raised in a bilingual household, they are at an increased risk of developing a speech delay or 'silent period' where they may not speak at all. While speech and language delays can occur in children who are bilingual, bilingualism itself is never the cause.
Sometimes delays may be a warning sign of a more serious problem that could include hearing loss, developmental delay in other areas, or even an autism spectrum disorder (ASD). Language delays in early childhood also could be a sign of a learning problem that may not be diagnosed until the school years.
The Disadvantages:
Children raised bilingually run the risk of not mastering either language, and subsequently having difficulties in successful completion of a formal education.
On the other hand, some of the disadvantages of bilingualism are an apparent delay in language acquisition; interference between the two phonological, lexical, and grammatical systems; and a possible decrease in vocabulary in both languages.
Con: Less verbal communication
The truth is that learning more than one language at a time will also weaken your verbal skills. While you will learn a lot of interesting words and uses for your new language, you will also have the “tip of the tongue” problem regularly.
If a child is 15 months old and isn't yet speaking, it's a good idea to get a speech evaluation. So if your toddler is 2 or 3 years old and isn't yet talking, it's vital to go ahead and speak with their pediatrician, or with a speech-language pathologist.
Ideally, as children age, their speech intelligibility should be increasing. According to data presented at the 2003 American Speech-Language-Hearing Association convention, the typical norms you want to look for in a child are: 26 - 50% intelligible by age 2.
At 2-3 years, vocabulary keeps growing and includes many different types of words and sounds. Toddlers are still mastering difficult sounds, but you can understand more of what they're saying. Toddlers are learning to make three-word sentences. Conversation skills are also developing.
A typical 2-year-old can construct sentences of two or three words, often without a verb. For example, a child might say, "There cat" for "There is a cat." Gifted children, however, will often be able to speak in fuller sentences at age 2. By age 3, a gifted child's language may already resemble adult speech.