The correct answer is the process of assimilation.
Assimilation is the name of a process children go through as part of their cognitive development. According to the psychologist, Jean Piaget, assimilation is a stage of cognitive development that involves applying previous concepts or knowledge to new stimuli or information. In this scenario, Sarah first thought that her brother's flute was a whistle because she had pre-existing knowledge of what a whistle was and applied that knowledge to a new, similar object- the flute.