Design a multilingual education
I think, I did something different in his education compared to my Chinese acquaintances whose children became passive bilingual in this English dominant society: Firstly, he didn't attend a preschool before three. We did our best to establish our languages during the first three years, which are the crucial time for development of language. We didn't teach him any English before he has enrolled at preschool. Besides, we are a non TV family and his exposure to English is limited. He learned English merely by picking up from his surrounding.
Secondly, he attends a part-time program. In other words, he spends longer time at home with his parents than at school with his English peers. Thirdly, I read only Chinese books to him before he turned three. His father tells him stories only in German. In this way, we can ensure that he is exposed to Chinese and German sufficiently, is able to communicate in our proper languages and not in a mixed language.
Individual trait of linguistic cognition
Further he possesses a distinctive way to conceive his multi-linguistic world, especially as an infant. Before he turned four, it was astonishing to observe that he believed, I couldn't understand another language than Chinese and my husband than German. Mysteriously he didn't believe that in fact my husband and I communicated only in German to each other. On the contrary, he believed that my husband and I didn't communicated at all. He might perceive this fact because he understood what we were saying, but he didn't realize it.
If we told him we were speaking in German to each other, he insisted not to give up his false belief. He became upset if I spoke German or English to him. Since a half year he has realized that actually both of us are able to understand all of these three languages like he, but he keeps his speaking habits and doesn't use this enlightenment to spare his learning. Like before he continues to learn our languages diligently and insists that we shouldn't speak other languages than our mother tongue to him.
After he enrolled at preschool, everyday I read English books to him. Curiously he doesn't consider reading as an act that directly addresses to him. On the contrary, he ignores the fact that everyday I read English books and teach English reading to him. His multi-lingual world exists in a distinct way: He supposes that all people speak and understand only one language: his mother Chinese, his father German and the others English. At this age it seems that this fact and his weird belief wouldn't have any conflict to each other and peacefully coexist in his mind. I hope that he would keep believing it for a long time.
An additional language
From the efficient result of his early trilingual acquisition, I perceived that he might be talented in learning languages. In his education I need to do something special in order to maintain his languages on the one hand and to teach an additional language on the other hand. When he turned three and a half, I tried to introduce some Japanese to him.
At the beginning he resisted that I spoke a strange language to him, and then I used the previous "English model" to teach him Japanese. As mentioned above, he considers that story telling doesn't address him directly. He accepts that I read English books to him, although he doesn't accept that I speak English to him. I used this model to teach him Japanese. I downloaded a lot of Japanese children's books and read them to him.
After a half year he has really learned some Japanese. He needs Japanese playmates to use what he learned. I tried to find a Japanese playgroup in Tallahassee but I didn't find anyone. Right now we are intensively focusing on English reading and I've already stopped reading Japanese books for a while, but he keeps watching a Japanese cartoon designed for preschoolers. I hope, I will continue the Japanese lesson after we move to Germany and find a Japanese playgroup for him. Recently I am even thinking seriously about if we should enroll him at a Japanese elementary school, then he would learn Chinese characters at school and it could facilitate Chinese reading.