Is your kid still in this school now? I saw from their website that they have Chinese lessons starting from K1. My only concern for this school is about learning Chinese. Does your kid attend the extra Chinese lesson? Is the standard enough for them to catch up later in primary?
We used a similar approach. So my son picked up English first. But now, he sort of have picked up Cantonese as well (after my maid went back to Indonesia for a 2-week holiday) ... But then, my boy now speaks more Cantonese than English... which is not so desirable at school. And I have slowly given up talking to him just in English...
I know when he faces his teachers, he automatically switches to English. However, his grammar is not that correct. His Cantonese grammar is very good, without anyone teaching him formally. I could see the magic of "mother language"!