Indigo, thanks you so much for all the info!!!
I live in California, homeschool is allow, I actually did think about it but I am worry that it will limited his English learning and social time. (Not many ppl homesch in my city). I am now also looking into private school option too, but it is so expensive :<
Tigerle, thanks for your advice, my son is in play-base preschool, so he is doing fine in sch and enjoy the sch days. He did read/decode some english words/sentences(e.g. It is a cat), but still not yet speak in sentences. For the public school in my area, most kids are asian, so I believe they are familiar with kids speaks ESL.
You are right, I also worry that the school will give him lower level work bc of his english.