At time of writing my son is almost three-and-a-half, and my daughter is one-and-a-half.
Jake's English is exceptional, but he was slow to get started. Jake learned English vocabulary, structure, and some accent according to the Thomas the Tank Engine method.
He is now inventing words. My favorite so far is ignoying, as in "Daddy, stop ignoying me", to which I sometimes respond: "Jake you're ignoying me, too". I think it's a keeper. I must start using it around work :-)
Ella, on the other hand is more precocious, already saying many words and even a few two word sentences: "Herro Daddy". I have started trying to speak -- and latterly learn -- Hebrew in an effort to get Andrea to talk to the kids in her fluent Hebrew. It works this way: I speak in broken Hebrew and Andrea corrects me, and is reminded to use it a bit more, and apparently feels less self-conscious about her (perceived) lack of vocabulary.
[I am now trying to learn conversational Hebrew, and am enjoying making some progress, although I seem unable to reproduce the guttural "r" for love or money.]
Ella is already saying "Toh-dah!" (thank-you) with aplomb. Jake is more cool, sometimes imitating, but sans enthusiasm, and sometimes saying, "Don't speak to me like that!"
I think that if I keep talking Andrea will keep speaking and Ella will learn for sure. As for Jake, on this issue at least, I intend to continue ignoying him.