It has been proven that the more proficient children are in their native language, the more success they'll have acquiring another target language which, in this case, is English. One's native language, and accent, is a big part of one's identity. Those should not be discarded; instead, they should be embraced and celebrated!
According to cognitive neuroscientist, Ellen Bialystock, the evidence is in the BRAIN!
Having our families maintain their native language at home is important! Read Claudia Dreifus' article from the NY Times on The Bilinguage Advantage.