My thoughts on this: Set up a nepali period in the evening and few hours during the weekends. During this time, teach the kids nepali, reading and writing. Once they start reading, get them books to read and a dictionary. Talk to them in nepali. Many US college students have good spanish speaking skills after taking few years in highschool and college. So I think it is possible to teach them nepali. As far as proficiency goes, I don't think they will be proficient as you are. Don't you think that after studying and working in US for several years you are able to put your point across if you spoke or wrote in English than in Nepali? Many parents speak to the kids in English because it is easier for them and the kids. They don't have patience to make them understand what each nepali word means. So I think if you have will and patience, your kids will speak in nepali to some extent.