We live in the UK and are a German/English bilingual family I practise OPOL and DC (7 and 4) are fluent with both still prefering German over English.
Now DD (4) is very interested in reading and writing. I now the advice is to let them learn to read in one language first and then teach them to read in the other. This made sense for DS (now 7) who had no interest in that sort of thing, and also he was quite young when he started Reception.
DD will start school next Sep, and I couldn't show/teach her English letter sound when the only language I use with her is German. My instinct is to just carry on with showing her how to write what she wants to write, telling her the German letter sounds and how to form the letters. I told her about a book I still had from DS (it introduces all the letters, shows how to blend them and has little game activities) - she was quite excited.
I'am planning to just follow her interests at home in German and then let her learn to read in school in English properly.
I would be very grateful for any experiences/advice.