Hi, what a good idea! I haven't read the whole thread but will after I've added my "grain de sel".
I'm French and speak French at home with my dd, who's 3.3. Her father is British but we're separated. DD is fully fluent in both French and English and she was not late speaking in either language. Before she could talk we did some baby signs (communicating with signs and gestures), and her father was doing the same, so she had the same sign for words in both languages, IYSWIM. I can't be sure but I have a feeling it helped her. At first she was mixing the two languages quite a bit but soon got the idea that they were different languages.
We go to France quite often and I try to meet with other French-speaking families. When we're outside and she hears someone speaking French she always comments on it. Our newsagent always says "au revoir" to her and that never ceases to delight and amaze her.
In February we went to Germany for a week and she was speaking with some people in French, others in English, switching effortlessly and never forgetting who spoke which language. She even picked up a few words of German! It's amazing how easy it is for small children to learn new languages. They are just sponges! My dd switches from perfect French to perfect Eastender, it's quite funny actually...
At home we have both French and English books, tapes, CDs and videos, for instance she'll happily watch a Winnie the Pooh video in French or English or even German. I read to her both in French and English but also read English books in French, translating as I go along. I always ask her which language she wants me to read in.
I myself come from a two-language family, with a German mother and a French father. I grew up in France and started out fully bilingual but my mother stopped speaking to me and my brother in German when I started going to school as she worried it might confuse us. I am not fully fluent in German, as I lack practice and vocabulary, but my accent is flawless. If I spend a few days in Germany it all slowly comes back. Still I wish my mother had carried on speaking to us in German, I'm sure she was advised to stop by well-meaning people
Someone (sorry can't remember who) mentioned a French school/nursery earlier on this thread. Where is that? I know of a couple of Saturday morning schools in London.