It does look ambitious, but it's been done before and there are many, many parents around the world doing it with their kids, even though they may be in the minority. This strategy is adapted from the OPOL (One Parent One Language) Method, where obviously one parent speaks one language exclusively with the child.
I would call Singapore one of the most unsuccessfully bilingual countries in the world. Why unsuccessful? Well, our bilingual education system has managed to churn out students who are adequately competent in English and grudgingly passable in a second language - Mandarin in the case of ethnic Chinese. To hear young Singaporeans speak English can be painful on the ears and in Mandarin, excruciating.
We have one of the highest literacy rates in the world, consistently come in first-place in annual global Math and Science high-school tests and are one of the few developed nations in the world that mandates bilingual education from kindergarten through to senior high school. We probably also have one of th highest rates of resistance towards Chinese-language learning in the world. In fact, Singaporean kids so loathe the mandatory tests they have to pass in Chinese and parents railed with such vitriolic against the uncommonly "harsh" and "stringent" criteria of Chinese competency in school that the authorities have had no choice but to modify (aka: dumb down) the Chinese syllabus for school kids not once but several times in the past 20 years. With each passing year, more people (usually parents of stressed-out only-English-speaking kids) cry for more breaks, from de-emphasising exams to doing away with the Chinese A-Level criteria for University admission - which, I believe has happened.
Let me say that such Singaporeans completely miss the forest for trees. They do not appreciate their great fortune for living in a place where bilingual education is the norm and where their children get a quality English and Chinese education in a social environment that supports bilingualism. Elsewhere in the world, in America, the UK and Europe, parents struggle on their own accord to give their kids a proper second language that the state education system does not. In Germany, primary school kids get a piecemeal few hours a week in English as it is taught as a foreign language. In the US and Australia, more and more schools are responding to demands for Chinese language education and parents pay big bucks to enrol their kids in charter (private, state-subsidised) schools that teach almost exclusively in Mandarin.
And here in Singapore, people complain bitterly about having to put their kids through supplementary Chinese classes, tuition classes just so they can pass their exams. I foresee the whining waning in the next couple of years, as the reality of a rising China has begun to hit the younger generation of parents like a dousing of cold water. In today's world, literacy in Chinese is a basic fundamental to get your foot in the door to any institution or business that wants in on the Chinese economy. It's not even an advantage anymore and it is rather a cultural understanding of China and Chinese history and society that might give you that edge over the thousands of white Westerners who speak the language.
Singaporeans just don't get it.
Back to our Great Experiment with Julien. Daniel and I are on the same page when it comes to language learning - if he has the benefit of coming from a family that speaks 3 languages, then we are fools not to give him those 3 languages. However, our experience with the respective education systems of our home countries has taught us some valuable truths about language acquisition:
1) Language fluency can only be attained if the language is spoken in the home environment by a primary caregiver;
2) Language fluency requires a supportive social environment: reading, mass media and oral communication
3) Language fluency is long-term capital-intensive investment - there are no short cuts and absorption by the child is usually tacit and indirect.
Being trilingual is not going to happen overnight for Julien. It requires from us a completely dedicated regimen and devotion to the OPOL method, bearing in mind he will have limited social resources for German and that I will have to make an uncomfortable 180-degree mental shift to using my second language - Mandarin - with him. But it can be done, and by sheer force of will or not, it WILL be done!

