I have also seen many nepali parents who still feels proud when their kids speak in english.  i always told them this, do not make this a big deal.  english is a language and even you dont want them to learn or speak english or learn western culture, they will eventually learn  in short period once they start going to school.  so, it is your duty to provide enough information about our culture, religion and speak nepali language at home and take to temples once in a while if you really want to them to learn about nepali society.  involve them in nepali gathering, encourage them to speak in nepali.  once they grow up, they will feel unconfortable to speak in nepali as they will have heavy accent, however, keep on encouraging them to learn our culture.  if you can, take them to nepal in vaccation.