Count yourself lucky if you have access to any form of immersion program in your minority language. The real advantage of these is that the child hears the language spoken by many different people and during a wide variety of activities. But, the "sink or swim" aspect of full immersion worries some, as does a value system rooted in a foreign culture.
The advantage of immersion programs
By far the best way for a preschooler to excel in a foreign language is an immersion program such as a full immersion daycare or preschool which can be especially useful if neither parent speaks the minority language. Why? For better or worse, your child learns far more from other kids than from any adult. So, take advantage of this when it works in your favor!
Immersion schools are an outstanding resource, provided the overall academic level is comparable to regular schools. If immersion programs are available in your area, take the time to visit and to seriously consider them. A second best option is to join or start a playgroup.
What to expect from full immersion
Children who have some foundation in a language can really hit the fast track when attending an immersion preschool or daycare. But even monolinguals do much better than their parents could ever hope. Most schools admit a good number of monolingual children with no prior exposure to the immersion language. The more a child without previous language exposure attends the better, but three full days per week is typically the minimum (or five half days.) It also depends upon your child's knack for language, motivation, outgoing nature, etc. Below is what you can expect from three days per week of immersion.
First month: Everything is new, and the child will resist the change vehemently. Typically, after the initial crying bouts, he may be quieter and more reserved than his normal self at school and may resist playing with the other kids. Remember that this sort of behavior is extremely common even if there isn't a new language involved -- it is a normal toddler reaction to any large change!
Second month: The child begins to adjust to the new situation. He opens up and plays more with the other kids and begins to learn the basic words (yes, no, food items, etc.) He begins to like and gain trust in the teachers.
Third month and beyond: The child becomes comfortable with the situation and starts to enjoy himself, really accelerating his language learning. He has made a few friends and looks forward to seeing them. (Remember, happy kids learn the fastest.) At this stage, he'll increase his vocabulary much faster and start to combine words into simple sentences, maybe even picking up some basic grammar. If you can keep up this kind of language interaction, you're really off to the races. After about one semester, he will be comfortable using the minority language and will be quickly catching up to his peers -- well on his way to speaking a foreign language, just by playing and having fun!
Reservations about immersion programs
Some parents would love to enroll their child at the local immersion program, but they still don't do it for a variety of reasons -- they don't like the program, the teachers, or the facility. The pros and cons of such a situation are highly individual, of course. In terms of the overall content of an immersion program, something many mono-lingual parents worry is "too much," meaning that a foreign language is one thing, but they worry about forcing their child to adhere to the cultural norms and values associated with the language as well.
"I'd love to have my girl learn Chinese, but I don't want her to grow up becoming Chinese. I really have a hard time relating to their value system. And it is not how I'd raise her myself," is one example. Or, "I feel like I'm sending my boy to Japan every morning. I'm not sure how good that is once he'll start regular school." Conversely, parents elsewhere in the world who consider sending their children to an American school to learn English worry about 'coca-cola culture', consumerism and a too competitive school environment. It is obviously the decision of each school how much they emphasize the cultural component, and some parent's will be all enthusiastic, whereas others will feel like outsiders in their child's upbringing.
So, if you disagree with aspects of the program, then what? Do you go with the language advantage and turn a blind eye to a culture that is foreign to you? Or do you nix the whole idea? The issue is probably a question of timing. If this immersion situation will last only until kindergarten, the child will be socialized many times over before he reaches adulthood -- and will still have established an incredibly solid language foundation. That foundation can then be maintained throughout childhood, without the need to continue the immersion program. Another major benefit in early immersion is the establishment of early and enduring friendships. After a few years in an immersion program, the child will gain minority language friends, further motivating him to keep up his language.
Again, the general rule seems to be the earlier the better if you are not sure about the immersion program. The further along the school system the child is, the more risk it involves, becoming increasingly disruptive in the education. With a preschooler you can afford to try out the program and see if the reservations can be outweighed by the gain in language skills. For older children you want to feel pretty confident that the program is right for your child not only in the language component, but comprehensively.