Children

I disagree, I think temperament changes a lot because it's influenced by a lot of surrounding factors like parents, culture, friends, educational environment
For example, a child born into a family full of love and upbringing from grandparents and parents will form a good temperament. On the contrary, if the family lacks love and care, the child's personality can develop in the negative direction
Or if a child learns in a good educational environment, with enthusiastic teachers, and sociable friends, their personality will become open, energetic, and positive thinking.