My daughter's first language was russian, but moved from Ukraine at age 2. My wife speaks fluent russian and english. English is my native language, and I speak russian as a beginner would.
Over the past 2-3 years, my daughter has learned english and refuses to speak russian. The period of 'code page' switching was short...and as many have observed, children have a preference to speak only one language.
This has been the experience of our russian friends too. In their homes, only russian is spoken by the adults, but the children, while retaining and understanding of russian, speak english in return.
on the plus side, I have worked on my accent considerably...worked on my daughters understanding that an english speaker could use some russian too (she really objected to me learning russian at first. My daughter has a keen sense of 'proper'...she thoroughly objects to me parking on the left side of the driveway, as an example...and did not appreciate my attempts to speak russian either)....but at long last, I too can speak to my daughter in russian at times, and she speaks back to me in english, same as she does for mama.
and my approach has been to realize she has lost her ability to speak russian natively, and have switched to teaching her russian as a 2nd language instead...this has provided for us an activity that we share, and she is really good at naming things in russian, when directly questioned.
She is even slowing coming back to say a word or two in russian, although in a nonsensical way, just randomly picking a noun to speak at an odd time...not a sentence or a complete thought.
anyway, thats our experience, her russian understanding is still astounding, and I often wonder why she can't just speak what she knows....but she doesn't and I guess, perhaps that is a harder skill for a child than for an adult.