Both Colin and Mary are greatly changed by their friendship in The Secret Garden.
At the beginning of the novel, Colin is so sickly he cannot get out of bed. He keeps the curtains closed and believes the light will make him worse. All he does all day is lie in bed and cry and complain. After becoming friends with Mary (and later Dickon), however, he changes. He learns to run and play outside. He realizes he is not sick like he has always believed. He becomes kinder to others and becomes truly happy.
Mary also changes greatly as a result of her friendship with Colin and Dickon. At the start of the novel, Mary is mean and unkind. She is rude to others and has no friends. Once she makes friends, however, she begins to change. She makes attachments to others and comes to love Martha and Dickon. She loves to play with others and helps Colin reach his full potential.
Friendship changed the both of them. Once lonely and unhappy, they are happy and fulfilled by the end of the book.
