I also don't think any country should be required or feel obligated to teach a parallel school curiculum to imigrants in their native tongue.
I'm not sure that any country IS required to do this. I don't see a problem with having bilingual teachers to help ease kids into learning English, but I haven't heard of (but wouldn't be entirely surprised) a school that is required by law to teach a parallel curriculum in a child's native language for their entire schooling lives.

That's just impractical and not desirable.

However, I do think that a smart country would invest in getting good ESL programs into their schools as immigrants are essential to economic wellbeing. When their ability to speak the most spoken language of the country is limited, so are their job opportunities.

That said, I think a lot of positive reinforcement about the importance of immigrants' native languages should exist in these programs. Too often, immigrants' desires to assimilate mean that their children lose out on their culture, as is your son's and son's father's case.