Learning of foreign language should start as soon as possible, the best time is to start this process in kindergarten.
First, there is mounting evidence that kids the best learns foreign language in kindergarten and in the future have better results in education that kids who started learn language later. Moreover, they can learn the correct pronunciation which can not be achieved at later age or could be very difficult.
Second, this method is very pleasant, kids learn through play. Also, kids speak fluently before primary school which can pay in the future through good and well paid job.
Third, children in young age experiencing new culture and laearns tolerance towards other country.
To sum up, learning of foreign language in young age is the best decision because it helps later in education and it is a method very pleasant for children.