This is why I took great effort to immerse my daughters in Mandarin Chinese and in Taiwanese (a Chinese dialect) at an early age. Since my kids are cross-cultural in more than one sense (their father is Korean while I'm Chinese.. and we're living in America!) I felt it was important and even useful in the future to be at least bilingual... but I'm hoping they'll pick up Korean, too. And if you count the Taiwanese dialect as another language (because I think Taiwanese and Mandarin is as different as Spanish is from French).. then she'd really be quadrilingual!
So they get the Taiwanese exposure from my parents and my older daughter is pretty fluent in Taiwanese. I know they will get English in school and she is already speaking mostly English because most of her friends at preschool, church, etc all speak English.. after all we are living in America. So I still try my best to speak to her in either Taiwanese or Mandarin Chinese because I know that some kids lose the ability to speak a language they once knew as a toddler after they are full time going to school. As for the Korean lanugage.. since dad mostly speaks to them in English, we'll have to have their paternal grandmother speak to them more and perhaps we'll have to send them to Korean school! Or we'll just have to hire a korean speaking nanny!
But especially with the way the future looks with China becoming more of an economic power... I think it may be really useful to be able to master the Chinese language. So we've been going to this "Mommy and Me Learn Chinese" class in our community for about half a year now. It is for kids age 3-5 and it is mostly just crafts and songs but it's exposure! The class was featured here. Come join us if you have Monday mornings free and live in the area!