I am teaching my DD Chinese and English at the same time. I can tell that she is picking up whatever is easier. She now just start to take interests in math. It's clear that she is into Chinese and will be learning in Chinese first (It's so much easier in Chinese than English. All numbers you need to know is 0-10, hundred, thousand, and 10 thousand. Each individual number is much shorter than English too. "lin, yi, er, san, si, wu, liu, qi, ba, jiu, shi, bai, qian, wan" That's partially why they test better too.) If you are teaching two or more language at the same time, how do you help them to understand math in both ways? To be honest, I had a lot of problems when I learn it in English.