You can send your child to afterschool programs or language schools on the weekend to learn a new language.
Errr... yes and no.
There is a world of difference between becoming bilingual through immersion (and K really is at the late end for doing that), and learning two languages in a school like environment. I learned English at school. I spent over a decade doing all of my recreational reading in English. I have been in the US for nearly 15 years. There is no way you could mistake me for a native speaker.
Except for a few people with exceptional language skills, native-like fluency is nearly impossible to achieve outside of early immersion.
I am not going to try and argue your nephew and niece's experience, although I am a bit surprised that kids whose passion is math/science would have limited themselves to what was taught at school -- or were they able to get all materials for personal investigations in French? (and in that case I want to know who their provider is!) It certainly sounds like the
school didn't its job properly (or were they being groomed for the French high school?).
I know our program spends a lot of thought trying to balance the needs of keeping as much Spanish as possible in the curriculum vs. making sure the kids are ready for English-only 6th grade.
One concern I have about the program you described is that it's 100% Spanish for two years. DS's school was 80% French/20% English for the first two years (more English later). The English component was mostly reading and spelling (but they had to do math, too).
Yes, that. It might mean that they won't have any native Spanish speakers in the program, which would be a red flag to me.
Most bilingual programs recommend going sequentially with early reading acquisition, to make sure kids don't mix up the phonetic rules of the different languages.
A point in Bostonian's article reflects our experience, which is that DS definitely had a smaller English vocabulary when he stepped into a full-time English-speaking school. But he is HG or more, and it wasn't a big deal. He caught up without any problems.
I think once you have the concept, adding the new word doesn't take much work (especially when a brain works with lots of side by side little boxes, like yours -- have you asked your kids about the way
they do it?).
I must say that the quotes from the study the NYT quotes make me think that like most studies of bilingual acquisition in the US, the subjects in the study were mostly low income/education immigrants families, and the confounding factors are... many. Because my kids certainly learned "astronaut" and "rectangle" in French at home before they entered K (I spend a lot of time and money finding and importing books), and their (English-only, private) preschool did cover "spatula" and "squash" in English before they turned 4.
And to answer Bostonian's question about why would anybody want to learn a language other than English... Because some materials you are interested in can be accessed faster, and without being mangled by incompetent translators? Because you want to spend some time in a different culture and it is impossible to do so without learning how to communicate with others? Because it is fun??
People interested by more tangible rewards might want to look at this:
http://languagelog.ldc.upenn.edu/nll/?p=8364But yes, the US is a big country, and if you are not interested in Russian literature, Japanese manga, or falling in love with a German Swiss you will probably be fine sticking to English
