From a parent's point of view, the most important and exciting thing about language acquisition is probably just that it allows their children to talk to them. But exactly what does it take to be able to talk? And how do children get from the point where they can't do it to the point where they can? Most children start producing words some time between the ages of eight and twelve months or so, and many children have ten words in their vocabulary by the age of fifteen months. Things gradually pick up speed from that point on. Whereas an eighteen-month-old child may learn only one or two new words a day, a four-year-old will pick up as many as twenty. (That's more than one per waking hour!)
ヶ月までには10個の単語を自分のボキャブラリーに持つようになります。その時点から状況は徐々にスピードアップしていきます。18ヶ月の子供は1日に1つか2つの単語しか新しく覚えないかもしれませんが、4歳児の場合は、20もの単語を新たに覚えます。（起きている時間で計算すると、1時間につき１単語より多くの単語を覚えていることになりますね！）
How does this happen? Adults don't pause between words when they speak, so how do cildren figure out where one word ends and another begins? How do they learn to make words plural by adding the suffix -s and to put verbs in the past tense by adding -ed? Why do we find errors like eated and goed? Why do children say things like I can scissor it and I sharped them? By themselves, words are just empty shells, and there's no point in learning a new word if you can't also learn its meaning.Children are remarkably good at this too - so good in fact that they are often able to learn a word's meaning the first time they hear it used.
for instance, a child who sees a horse running in a field and hears her mother say "horse" typically figures out right away that the word refers to the animal, not to its color, or to its legs, or to the fact that it's running. What makes this possible? Meaningful word are the building blocks out of which we create sentences, our princip;al message carriers. Most children begin producing sentences some time between the ages of eighteen and twenty-four months, at about the point where they have vocabularies of fifty words or so. First come two-word utterances like Mommy here and That mine, then longer telegram-like sentences that are missing little words like the and is as well as most endings .
有意義な単語は、主要なメッセージを伝える上で、文章を組み立てるために用いるブロックである。１８ヶ月から２４ヶ月目にもなると、子供たちは時には文章を作り始め、その時点での語彙は５０単語以上である。まずは「ママ、ここ」「それ、僕の」といった２単語の発話から始まり、次により長い、「the」（その）や「is」（てにをは）といった瑣末な単語が欠けた、電報のような文章となってくる。
By the age of three, the basics of sentence formation are in place and we find many sentences worthy of an adult - I didn't know that one stands up that way, Does that one get a button?, and so on. How does a child master the craft of sentence carpentry at such an early point? A whole different set of challenges face the child when it comes to the meaning of sentences. How, for example, is a child who can only say one or two words at a time able to make herself understood? How does she figure out that The car was bumped by the truck means the exact opposite of the truck bumped the car even though the words car, bump, and truck occur in the same order in both sentences?
Why doesn't The doll is easy to see mean that the doll can see well? And then there are speech sounds - the stuff of nightmares for adult language learners. Just how does a child go about distinguishing among dozens of speech sounds? And, equally important, how does she go about figuring out how to make those sounds and then assemble them into fluent melodies of syllables and words? What, if anyghing, does babbling have to do with all of this? Do children really produce all the sounds found in human language before learning to speak their own? All of which brings us to the ultimate question: how do children learn language?
訳で分かりにくいかもしれない部分の補足です：
The doll is easy to see 人形を見ようとする人にとって見やすい（見やすい位置にあるとか、簡単に見れる条件にあるとか）
The doll can see well 人形自体が主語で、人形の目がモノをよく見ることができる。
どちらかといえば、児様語(舌たらず言語) でこれらのことをやらなければならないのだろうか？子供たちは、独自に話せるようになる前に、人類の言語に登場するすべての音を発することができるのだろうか？これらすべてのことは、次の究極の質問に到達する。「子供たちはどの様に言語を学ぶのか？」
Every time I'm asked that question, my first inclination is to respond by simply saying that I wish I knew. In a way, that's the most honest answer that anyone can give. The fact of the matter is that we still don't understand how children learn language any more than we have figured out how the universe works or why we can't all live for two hundred years. But that doesn't mean that we are completely in the dark. On the contrary, research in the last three decades has yielded many exciting and important findings that reveal a great deal about how language is acquired.
