i personally studied chinese since kindergarten until form 5. at home i speak english. those who don't know that i've been studying chinese tends to think that i'm a 'banana'. and when they hear me speak chinese they'll be so shock. anyhow, my chinese isn't that good basically because i have not much interest in that language but at least i can read/write simple chinese and also speak proper chinese.

as for my brother, he studied in an english kindergarten and my mum sent him to a chinese primary school. during standard 1, he was crying almost everyday because he didn't understand a word in school or his homework. but after 3 or 4 months he got used to it and pick up chinese very fast. he just finish his UPSR this year and got all As, he speaks chinese to his friends just like any other students in his chinese school. now my parents sent him to new zealand for year 9.

my family is an english speaking family, my mum don't know chinese at all, she picks up little bit of chinese here and there from me and my brother when we were studying. my dad knows chinese but seldom communicate to us in chinese. so in my opinion, in your situation, its best to sent your child to chinese school so he will be exposed to the language and 'culture', which will really help in the future.