As a reading teacher, I have an interesting comment on this phenomena. There is a "dirty little secret" among the upper level society with children who are brought up with non-English speaking nannies and in houses with little give and take conversation. These kids are language deficient--as deficient as that typically seen in the worst housing projects. This type of deficiency requires immense exposure to language and many times the kids just never catch up.
Stay at home moms offer their children so much with the day to day conversation and things they probably just take for granted. A child who is spoken to and read to daily is often facile with upwards of 75,000 to 100,000 words before entering kindergarten. Language deficient children can be as low as 10,000. What a difference!
Is it hard to see which one will excel and which one will be trouble very quickly?
That's very interesting. Guess homeschool moms are doing more than they think!
Way back when in high school French class, my instructor, a French woman who became a US citizen relayed a similar story. They spoke English at home, but they hired a French nanny who spoke French to my teacher's son. He wasn't speaking for a long time. My teacher ordered the nanny to stop talking French to him and the son began speaking English very soon afterward. How confusing it would be as an infant to hear two languages spoken to you.