My #2 son learned Spanish from his friends across the street and others at school. He pursued it by dating Spanish speaking girls who were trying to learn English. Quid pro quo. His ability to speak Spanish was critical to being hired at Rubio's (his 2nd job in high school). Half the staff didn't speak any English.
I grew up in an immigrant community. I was born in Puerto Rico, but my mother was Brazilian. My mother never did learn much English. It was a very frustrating language for her. I learned English from watching cartoons and television, but missed much of my first and second grade years, because I didn’t understand a word that the teacher said. My children speak three languages, but only want to speak English. They rarely even tell others that they speak another language. This process is pretty consistent through all the immigrant communities I have been in. The adults don’t always assimilate, but the children almost always do. The bottom line is that children that grow up in the US, want to be completely American, whether their parents do or not.