I have 2 DC, and live in France with French DH.
We're doing a rough OPOL in that I only speak to the DC in English, DH only speaks to them in French. However I speak to DH (and everyone else) in French, so the DC know I speak both languages.
DH also speaks to my family in English so DC know he speaks both languages.
DC go/will go to a French school (eldest is in PSM).
For the moment we've been pretty relaxed about the bilingual side. Naturally we've got books and DVDs in both languages. English is definitely strongest right now but I'm sure that soon, with the school influence, French will take over. DC know which language to speak to which people (sometimes with a bit of prompting).
I'm wondering what to do later on when the DC start to learn to read/write. We're in Paris so there's lots of activities in English, including a very expensive course in English for bilingual children, which I've looked at but I'm not sure if it's something to start as early as possible (aged 5 for this particular course) or wait until DC are older and need more formal education in English, over and above what I can do naturally at home.
Are there any good reading materials on the internet/books on this subject that you have found useful?