Wow, that's really exciting! We did a similar thing recently and moved out there for a year with our kids who were then 4 and 2. It was amazing and we had a super year.
If it's only 6 months I would totally advise you to live centrally. It is much more normal for families to do that in Paris than in London and despite initially apoearances we found central Paris to be pretty child friendly. We lived in the 15th which I would totally recommend.
As for nurseries, I know lots of bilingual ones in the 15th but the 6 month thing might be tricky and most close for a couple of months over summer. Are you getting help from a relocation agent?
Best advise I can give is to join message.
http://www.messageparis.org/public_website/ an English speaking mums group which is very active. Once you join you can access their online forum which is very like this one.
Anyway, feel free to pm me with any questions