Adolescents who learn a second language often apply patterns of speech production used in their native tongue and thereby speak the second language with an accent. this phenomenon can best be described as an example of:

I believe the answer is: negative transfer

Negative transfers refers to the process when a new learning is creating an interference toward previous knowledge.
In the scenario above, the interference happen to the children due to the conflict in identifying two different language that  describe one same word/sentence.