The closest I can think of is the interactive Muzzy products. posted by radioamy at 1:31 PM on December 9, 2006
This post has some suggestions for magazines for kids in French. I think just having the magazines around the house will increase their awareness of the language.
Also, I asked a similar question about French print media for Anglophone teens a few weeks ago - just another data point. posted by mdonley at 8:08 PM on December 9, 2006
I don't know of a site specifically desinged to teach French but my two year old is picking up words from this site:
posted by radioamy at 1:31 PM on December 9, 2006