To Valda:

Turning back to the discussion subject, I would admit I partially agree with you.

But I think you forgot to mention one important difference between a child and an adult.
A child who is in process of acquisition of his first language, has a completely "clear mind", ready to accept any information. There is no "reference point" to him, the language he is learning in the language-speaking environment is the first and the only language he knows.
An adult is already fluent in his native language. And that is a "reference point" for him. A native language "dictates" how he is used to express thoughts. That is a significant obstacle to get rid of the native language habits and to get used to the foreign way of expressing thoughts.
According to the Sapir-Wolof hypotesis, our native language is what forms our "world picture". A child has no "world picture" at all yet, it is being formed together with learning the first language.

And I would say the "source" language (I mean one's first language) always matters when we learn a second language. For example, I see some errors in your latest post in Russian, and those errors show you used some calques from your native English. You subconsciously expect Russian to behave the same way as you are used to, but the reality is different. And you would need some conscious effort to "re-organize" your thinking.

I will explain your errors in another post.