As baby's thought processes develop, we look back to Piaget. He called the stage between the ages of 2 and 6 preoperational intelligence. It is a period of incredible self-centeredness. Centration is baby's tendency to only focus on one idea, one part of something. She excludes any outside possibilities. For example, Daddy is Daddy only - he cannot be anyone's brother, uncle, or anything else because he is her Daddy. This also exhibits egocentrism - she only thinks of the world from her own perspective. You've probably noticed that by now.
She also has a tendency to focus on only what she sees. This is called focus on appearance. If something is not apparent to her, she generally won't think of it. This is in part because of static reasoning, a characteristic that means a young child thinks that nothing changes. What she sees is what she gets. Another characteristic related to this same mindset is called irreversibility, the belief that things cannot be undone. A snowman cannot become snow again. One 4 and 6 are 10, they are no longer 4 or 6, nor can they ever be again. Part of this can be seen in the "just right" phenomenon, for example, a tomato touched her sandwich and it is now inedible, the tomato cannot be removed.
Yet another related characteristic of logic is known as conservation, but baby will not master this until she is 6 or 7 according to Piaget's research. Conservation is the principle that a substance has the same amount even if the appearance has changes. For example, if you have two balls of clay that are the same size and you stretch one out into a long skinny piece of clay, baby will think the long skinny clay is more clay than the ball, even though she saw you change the shape.
Research by others has shown that children do much better on nonverbal tests or in game-like settings, but this is not the fault of Piaget; he worked with the technology available to him.
The final aspect of preoperational thought is known as animism, the belief that children have that inanimate objects are alive. Flowers, trees, stuffed animals, and even clouds have thoughts and feelings of their own. Of course, baby's thought will be influenced in the way she treats things, by her culture and her upbringing.
Leo Vygotsky, another famous cognitive developmentalist, held a more social view of baby's cognitive processes. He believed that many young children are apprentices in thinking, that is to say a child (or any person) whose thinking is stimulated by their elders. Normally for baby, you (and her other parent) and any of her siblings will be her teachers. Vygotsky believed that children learn because their teachers (parents, siblings, friends, etc.) present challenges, offer to help, instruct, and motivate. Another vital part of Vygotsky's idea is called guided participation - the way people learn from others who guide them. This is essential for baby as she explores her world and copies what she sees, looking for feedback.
A key to Vygotsky's theories (that you may have heard of before) is called the zone of proximal development. He believed that in the zone of proximal development are skills that a person can only do with assistance, not by themselves. It is important to look for those things that baby can't quite handle on her own and help her with them. This is called scaffolding - temporary support tailored to help her work towards mastery of a skill.
Vygotsky also had a few theories about language as a learning tool. He called the private dialogue that children use private speech; this is a tool that can help anyone work out new ideas. As baby talks out loud to herself, she is reviewing things she has learning, making decisions, and explaining events to herself. She may be unaware that she does this, but most people do engage in private speech. It should not be discouraged as it aids cognitive development.
Both developmentalists understood that baby is actively trying to understand her world. A theory related to this is called theory-theory, the idea that children attempt to explain whatever they see or hear by coming up with theories. Around age 4, baby should develop a theory of mind - that is a theory of what someone else is thinking. Before that age it will be impossible, because she will not yet realize that other people have different thoughts.
Back to language. Vygotsky's theories only explain a little of how language helps baby cognitively. As a 2-year-old baby will use only short sentences. She will have a vocabulary of anywhere from 100-2,000 words and she will use a lot of nouns, some verbs and a few adjectives. You might get asked a lot of "What's that?" questions. At age 3, her vocabulary will expand to anywhere from 1,000 to 5,000 words and her sentences will become more drawn out, to about 8 words long. She'll start using conjunctions and adverbs and you can expect a lot of "Why?" questions. By age 4, her vocabulary will be anywhere from 3,000 to 10,000 words, sentence length can jump up to about 20 words and she'll start adding tags to the end of her sentences, such as "...won't you?" The "Why?" questions will continue and be supplemented by "How?" and "When?" At age 5, her vocabulary may not even give her away as being a baby. Her vocabulary jumps to include anywhere from 5,000 to 20,000 words and her sentences will seem never-ending. Her grammar will become complex and she will start to notice and ask about differences (i.e. rich vs. poor).
Young children use a language technique that allows their vocabulary to expand rapidly called fast-mapping. When baby hears a word, she will automatically sort it in her brain and store it with seemingly similar categories. For example, if she hears someone yell, "Jerk!" she will recognize it as a derogatory term and file it away in the hypothetical box of "Things to Yell at Mom When Mad." Or she'll see someone point to a funny color, call it "maroon" and it will be filed away in the box labeled "Colors" somewhere between red and purple.
The grammar of language includes structures, techniques, and rules that make it possible for baby to speak properly. By age 3 she will understand the basics of grammar, and as she tries to apply it to her speech, she will make some obvious mistakes. One common mistake is called overregularization, a tendency to apply the regular rules to the irregular words, such as tooths instead of teeth and goed instead of went.
Language at this point is in a sensitive period, and beginning a second language is not a bad idea at this stage (for my full research paper on this topic click here). Many say that children should learn one and only one language, but research shows that young children can master two distinct sets of grammar and vocabulary along with the proper pronunciation and characteristics of both languages. Young children who become bilingual find it easy to switch between the languages, almost like a switch, and they are not confused when speaking to someone who only speaks one of the languages. The pronunciation becomes particularly hard to master after age 6, so now is a good time to expose baby to another language. It should be noted that TV is not a good second language teacher - it cannot personalize instruction for baby or engage her zone of proximal development.
Language and culture are deeply intertwined. Much of the bilingualism debate has to do with pride and cultural identity, but the political position only makes a mess - the cognitive benefits of bilingualism are clear regardless of political standpoint. Children who speak two languages are less egocentric than their monolingual peers and are more cognitively advanced in their theory of mind. While some skills may seem to come at a lower rate, bilingual schools in Utah have proven that there is nothing to be lost by learning a second language.
Some minority language children may experience a language shift, that is a shift from their first language as the primary to their second language becoming their primary language, but parents of minority children should note that this shift is mainly verbal, their comprehension is still very high for both languages. They should also note that balanced bilingualism is possible - baby can be fluent in two languages without any problem.
As you prepare to put baby in school, you'll find plenty of programs and they may be a little confusing to sift through. A child-centered program means that baby's growth and development are the focus of the classroom. The children follow their own interests rather than following adult instruction at all times. They are given opportunities to be the creative creatures they are. A Montessori school (named for the Italian developmentalist Maria Montessori) is one type of child-centered program that emphasizes pride, accomplishment, and tasks for baby and her peers. Another is called the Reggio Emilia approach (named for the town in Italy where it originated) which emphasizes creativity and personal learning needs. A teacher-directed program stress academics taught by one adult to an entire class. The teacher works to get children ready to learn in elementary school.
Project Head Start is a program designed for low-income and minorities who are thought to need a "head start" on their education before elementary school. The quality varies, but the program has provided education for millions of 3- to 5-year-olds. The idea of head start is to narrow the gap between 5-year-olds by the time they enter elementary school, but the political winds of change often shift the goals of Project Head Start.
What you should look for in a preschool is safety, adequate space, a low child/adult ratio, trained staff, a good curriculum, and positive social interactions between children and adults.