9. This is the first stage of development, which begins at birth and continues up to about age 2. In this stage, children learn about physical objects and are concerned with motor skills and the consequences of some of their actions. Whenever the children see a new object, they shake it, throw it, chew it or put it in their mouth simply, so that they may understand its characteristics. Around age 1, children learn the concept of object permanence i.e. an object continues to exist even if it out sight of a child.
11. This is the second stage of development, beginning around age 2 and continuing up till age 6 or 7. This stage is marked by acquisition of language and during this stage children become able to think of symbols, to form ideas from words, etc. Children, in this stage, also begin to understand concept of space and time and understand numerical concepts like addition and subtraction, they are able even to differentiate between past and future although they remain highly focused on the present. They focus more on concrete physical situations and have difficulty in dealing with abstract concepts. The thought of a child at this stage is very egocentric and often assumes that people see situations from his viewpoint.
13. This is the third stage of development, beginning around age 6 or 7 and continuing up till age 11 or 12. Children are now able to group certain things into categories, and put objects into size order, number order, and any other types of systematic ordering. There is a form of logical reasoning and thinking. Their experience of the world at this age makes them able to imagine events that occur outside of their own lives. A capacity for abstraction is also acquired at this stage and children begin to study complex disciplines such as mathematics, solve problems with number and reverse previously performed operations. The children are able to understand views and perspectives of other people and are capable of concentrating on more than one thing at a time. In this stage a child can do mental operations but only with real concrete objects, events or situations.