I think they should be taught English in school. If the parents want them to remember how to speak their "mother tongue", they can use it at home. I didn't grow up in an area where a lot of people spoke Spanish, but there were many other "mother tongues" kids spoke. Italian, Polish, and German are just a few. Other than German, Spanish, and French, no other languages were offered at our high school - and Spanish was NOT required. So I think if Spanish isn't available at the school for whatever reason, teach them at home.