As we know children are good at copying the deep or meaning srtucture of a sentence or message and they do not imitate the surface one.
I'm not sure that we do know that. Do you have an example of exactly what you mean?
I would like to know about an eight-year-old child who mimics the conversations whilst watching a movie in another language. Does she understand what the artists say?
If she doesn't so, why today researchers believe that children do not copy of the surface structure?
If they say this, they are referring to the child's own language.
What evidence do they give for saying this?
Child: I sawed a puppy!
Mother: You saw a puppy?
Child: Yes, I sawed it.
This 3-year-old is not copying the surface grammar, but is still using a past tense form. Is that what they mean? But by age eight, a child should have proper surface structure.
How can she distinguish the sounds produced by someone else in a foreign language?
She can't. Is anyone saying she can?
I would appreciate it if anyone can help me out!