When my daughter was 11 years old, she showed a keen interest in supervising her 9-year-old brother. Summer played the role of “the responsible older sister,” vigilantly hovering over her little brother. Ryan played the complementary role of “the forgetful little brother.” Summer’s eagerness to be her brother’s keeper made me uneasy at times, but I often found myself reinforcing their respective roles. This is how it went one afternoon: