I speak Swedish and my husband's native language is English. When we had our two children, we had no doubt that we wanted to raise them with equal access to both languages. Now, years later, when I've made promoting multilingual child-raising not just my avocation, but my vocation as well, people ask me for the straight story, warts and all.

"What is the difference, raising bilingual children?" "What do you wish you knew before you got started?" It's clear to most of us that speaking multiple languages is a good thing, and learning multiple languages in the early years is a nearly effortless means to fluency.

Your multilingual child will have a head start in schools during a time when more and more of them are requiring a foreign language. And once your kid knows two languages, the move to three, or four is much easier.
Counterintuitively, the effects of growing up bilingually include superior reading and writing skills in both languages, as well as better analytical, social, and academic skills. Parents who are themselves involved in high level careers are already well aware that professional prospects abound for those with fluency in multiple languages. Helen Riley-Collins, president of Aunt Ann's In-House Staffing in San Francisco, who caters to many clients in high tech, investment banking and finance, says that more than half her clients request nannies who speak another language. "They want to give their children a head start in business in 20 years." So, that all sounds well and good, but what are the real drawbacks?

Delay. Multilingual children tend to speak a little later than their peers. Although there is no solid scientific evidence to suggest a delay in speech, anecdotally there is a real sense among parents that multilinguals start talking three to six month later than monolingual children. If you think about it, it makes sense that a child learning two or more language systems might take more time, since they are actually learning twice as many words. But rest assured, even if your child did not walk at nine months, eventually he ended up walking just as well as those precocious ones. The same thing holds true for language, even when you are talking about more than one. Guaranteed!

Mixing. Children learning two languages often slip back and forth between them, mixing up their words. This can disturb the parents, but can be even more alarming to the uninitiated. No worries. This tendency will pass once the child has built a large enough vocabulary – around the age of four or five. Remember that the monolingual three year old often struggles to find the right word, and, for that matter, adults don't always find it easy to express themselves. In some ways, the multilingual kid has an advantage -- if he can't think of the correct word in Vietnamese, for example, then he can say it in English. While the rest of us are speechless.

Effort. Perhaps the most easily overlooked drawback to taking the multilingual path is that it requires more effort on the part of the parents. Raising a multilingual child is a commitment. Much like piano lessons, you can't expect your little one to be a virtuoso overnight. Language learning is a long-term investment in your child and will require that you are able to provide enough language exposure. At times, you'll probably need to boost the second language and offer some extra encouragement. You'll need the persistence required to keep your family language rules as consistent as possible. But, if you can keep faith for the first four or five years while a solid language foundation is put in place, things get easier. Incidentally, the multilingual second child is a breeze, if your first child was raised that way. Your first will end up doing a lot of the work for you by simply being a natural chatterbox.
There's no doubt that multilingual children have more advantages, but it can feel a bit overwhelming to someone already struggling with diapers and feeding schedules; however, I have yet to meet a single parent who regretted the decision. But, the appreciation from your child, as usual, is probably another 20 years out.