early second language learning

I've tried speaking in German to Helen a few times in the last week and she's really fascinated by it. If I stop she says "say something" and wants me to keep going, and this morning she requested some German quite spontaneously. And Camilla and I have started thinking about the options for her to learn a second language.

The primary schools we've seen offer French (but I think for years 5 and 6 only) and my sister Jenny's family speaks that at home, so that's the most obvious option (Camilla has school French and I can read it well enough to get around museums). Cantonese, Polish and German are the languages we have historical connections with, but neither of us speaks any Cantonese, Camilla has "kitchen" Polish and I have academic German (I can read it relatively well, but find speaking hard).

There's no way Helen is going to get enough language exposure to be bilingual, but I think a bit of early second language acquisition, treated as a game rather than any kind of chore, might be a lot of fun and might help lay the foundations for later more formal learning. I could try to organise playdates with Nina​ and Max and Lukas, but I suspect that would be more useful for me than for Helen - hearing other people speak a foreign language amongst themselves is completely different to having someone try it with you. Lucy​ says that Rachel gets upset if she speaks Russian to shopkeepers (which seems quite natural to me). And Helen has never shown any interest in Jenny and Thomas​ and her cousins speaking French to one another.

So do I persist with the German or do I maybe try to teach myself to speak French alongside Helen? I suspect we need to decide this soon, otherwise she's likely to get confused by us switching languages on her.