Occasionally, though more often than you would think, I have people ask me about the drawbacks of early childhood language learning.  Now, there are two problems with this: (1) I'm not an early childhood researcher, and (2) I've never really heard of any drawbacks.  Most TESL/SLA texts focus on the benefits of language learning/acquisition, specifically in foreign language context).

So here are a couple resources that describe some of the assumed and supported benefits.

Early Childhood Language Learning

• Raising Bilingual Children: Common Parental Concerns and Current Research
• Top Ten Benefits of Early Language Learning
• Early English Immersion Vital (I wanted to include a Korean source, given my location. Plus, she's a colleague) 

With the amount of support for early childhood language learning, I would enthusiastically recommend parents consider this with their children.  I also feel better about my very necessary approach with my own son (Korean/English). However, I have to pause a little.  One thing that I am suspicious about is the LACK of research on the drawbacks. Every topic out there seems to have at least a little support for each side, but I wasn't able to find anything (in a quick search) to discuss the negatives.  Why is that? There are always drawbacks, aren't there?

There is some research that describes problems inherent with children not learning their parent(s) language(s). This is certainly a concern of mine, but this shouldn't be a concern for Korean-speaking parents in Korea. No matter how good or intensive your child's language school is, they will not "lose" their Korean. This is the problem I hear cited the most from parents (and students) here in Korea. As far as I can tell, there is no research supporting this.

The other concern that I hear is that learning a language (in this case English) will cause children to not appreciate Korean culture.  This one could be correct, I guess.  Not that they won't understand Korean culture, but that they may have different expectations in the ways in which people interact (turn-taking, holding the floor, power, status, deference, etc.) that are influenced by their other language.  Not that I really think that this should be a concern, but I guess I can see it as a possible drawback.

If you have anything to add, please post in the comments. My understanding of language and social theory in this area is not well-informed.