A child's behaviour develops from infancy into the teen years. This development is a result of a growth in motor skills, language, and social skills as he begins to explore his surroundings. His behaviour will change at various stages through adolescence.
Infancy (Ages 0-18 months)
In the first years of life a child learns how to control his body and create relationships with the people around him. He will form a strong bond with his parents and siblings. He will become interested in his surroundings as he starts to reach for objects at 6 months old. By the time he is 1 he will be able to walk and explore the room he is in. His behaviour can be reckless at times, such as running into a road. He will behave negatively toward other children and may avoid playing with them. He can be moody and cry to get your attention at 18 months old, as his language skills are not fully developed.
Toddler (Ages 2-5)
A toddler starts to exhibit a change in behaviour toward other children. At age 2 he still prefers to play on his own and therefore can be selfish with his toys. He may become angry and throw a tantrum if you try to encourage him to share. However, his behaviour toward you will be positive -- he still likes to be hugged. His social skills will develop significantly when he is 3 as he starts to play with other children. As he turns 4 he'll know how to be friendly to others and take turns playing.
School Years (Ages 5-9)
When you child enters school his behaviour will be settled and he will adapt to being in a new environment. Between the ages of 5 and 6 he will like to be given chores, such as helping with meals and grocery shopping. Friendship will become important and he will soon have a best friend. However, his behaviour at times can be selfish and he will change friends often. At age 7 he will understand the concept of right and wrong. You can manage his bad behaviour by reminding him of the consequences of his actions.
Adolescence (Ages 10-13)
From age o 10 your child's hormones that start sexual maturity begin to work. His body will start to change as he grows taller and his voice changes. Girls may begin their period as early as 10 years old. He may become self-conscious if he is much taller or shorter than his peers. The changes in his body may cause him to have mood swings. At age 11 you will begin to notice that he doubts your beliefs and is easily influenced by his friends.
Teen Years (Ages 13+)
As your child starts puberty his behaviour will change. From age 14 he may stop hugging or kissing you in public and appear more interested in spending time with his friends. He will want to be treated like an adult as he becomes more self-reliant. He will rebel against your rules and structure even though he needs them. From the age of 13 his sexual development will begin. He will start to believe in love and find himself attracted to the opposite sex. At the age of 15 he will want to experiment sexually.