When we were moving to Canada with two young kids, I was first wondering whether we should put our kids into language classes. People who shared this experience told me not to bother. And they were right. The kids picked up the totally new language in no time. At first they were a little shy, not so much talking in English but understanding a lot after a few weeks already. Once they started Kindergarten they really took off. Within two months or so, they were fluent. We have to make an effort to keep up their Dutch now!And it gets better. Bilingualism seems to have mostly positive effects. The BBC recently published an interesting video by Ian Lacey about bilingual brains.
It talks about several benefits. Firstly, the constant switching can enhance other brain activity and lead to better focus, multitasking and better memory. One study measured greater density in the gray matter of the brain. Another benefit is that especially younger children develop strong empathy as they are able to communicate in two or more languages and apparently are better able to see from another perspective.
A lot of study is being done on these issues and scientific evidence is not yet conclusive. One Indian/Canadian study that is more conclusive has focused on the effect of bilingualism in later life. People develop dementia about five years later than non-bilingual people. So, bilingualism helps slow down the aging process and delay the development of dementia.
So, while learning languages from a very young age, it is never too late to start!