Many popular stories for adults and children are written in a series.
That means that the same characters are used in stories with different plots.
Many adult and children mysteries are written this way.
Children particularly like stories in a series.
This is especially true of picture books and middle grade stories.
Children seem to form an intellectual and sometimes an emotional connection to the main characters. These characters almost become 'friends.' This creates familiarity, and enhances the child's sense of security as connected with reading. Something (the characters) about the story is already known.
In addition, children who enjoy a particular book tend to want to read "further adventures" of those characters.
This is not to say that adults and children read series books exclusively.
Adults and children read many books that are not in series.
However, many adults and especially children enjoy stories in a series, and often stick with the series for awhile.
Click to look at some picture book series:
