Kindergarten and all the rest is Japanese only. The moment Sophie sees me she switches visually. By means of visual switching, locking her into a mode, it establishes an expectation and also a routine. For my daughter I am her English environment. She will always know to expect English.
Bilingualism is simply a kind of art, learning another method of artistic expression.
Whether you're a child or adult bilingual you quickly realize this. That's why people like knowing foreign languages or dialects. It's picking up new brushes and paint. It's part of the art of making yourself. I'm building a data-base for a dictionary.