There are such neighborhoods, but here's how it really works:

First Generation: Aren't comfortable with English, but usually the father figure in the family is fluent enough to hold down a job.

Second Generation: Fluent in both tounges.

Third Generation: Speaks English only.

Remember, the kids have to go to public schools who only teach in English, so while their native tounge might be spoken in the home and on the street, they still have to work, and they still have to leave the 'hood for things they can't get there. They MUST know English or a have a kid they can send to run errands for them.