May I state my opinion about child brain? Being a father of two children I can say that the learning of the native language isn't that easy and fast for a child. Let's take for example pronunciation. My son at the age of 5 couldn't pronounce sounds "р", "ш", "щ". And at a year earlier we had problems with the hard "л". My daughter also had similar problems. The right use of grammar also doesn't come instantaneously. A person's own vocabulary is accumulated during all of his/her life. For example the average vocabulary of a person at the age of 40 is almost twice as much as of a 14-years old one. Children learn their native language gradually. But they don't notice the difficulties because their intellectuality goes abreast with their language. When an adult person learns a foreign language there is on contrary a great gap between his mental power and the poverty of his speech, which makes him suffer. Moreover there are a lot of phrase templates of his native language in his head which are always ready to help, but suddenly they appear not to work in a foreign language. So the knowledge of the native language becomes an obstacle.