An interesting article. The important point is this:

Dr. Muñoz makes the point that children are only sponges when they get deep and meaningful exposure to the language. “You need a high frequency of input, of good quality,” she said. “You have to live with the language, use the language and function in the language.

Immersion is that deep and meaningful exposure. It’s why a taking Mandarin classes in elementary school (called FLES, for Foreign Language in Elementary School and usually 3-5 hours a week) doesn’t do much at all.

The article also reminds us that children go through a silent period when they’re absorbing  a new language. We don’t notice it when they’re babies because, well, they’re babies. But we do notice it when they’re give.

And yet pay attention to how much of what’s being said in your child’s classroom they understand. Do they get up when the teacher says to get up? Do they go to the sink to wash their hands when their teacher says to? Do they take out their math books and not their science books when asked? That means they’re understanding — even if they couldn’t say those sentences themselves.

It’s also true of English, when you think about it. Kindergarteners don’t say things like, “Could you please get me a cup of water when you’re finished doing the dishes?” But they understand us when we say, “Put your Legos away and after that you can bring me a book and I’ll read it to you.”

Do Children Soak Up Language Like Sponges?

A pervasive idea assumes that young children can absorb new languages with minimal effort, but it turns out that the science is more complicated.

When my husband and I decided to pack up our comfortable lives in Austin, Texas, to move to Barcelona, Spain, we had a dream for our then-3-year-old son: He would become trilingual. In Barcelona, most people speak Spanish and Catalan, the regional language. Speaking three languages seemed like a big goal for a small person, but we believed it was possible because of one phrase: Children are like sponges.

Whenever we told people about our plans to put our son in a Catalan school, they told us about sponges. Children learn languages quickly, they said. He’ll be speaking like a native in no time.

But that’s not what happened. In September, our son started school. It wasn’t until March that he uttered his first full sentence in Catalan: “M’he fet mal” (I’ve hurt myself). But that didn’t open the floodgates of language. His teacher assured us that he understood everything — he followed directions well, and he was learning. But he stayed mostly silent. I began to worry that my child was not as sponge-like a learner as I’d been led to believe.

Please read more here.