One summer evening during a violent thunderstorm a mother was tucking her small boy into bed. She was about to turn off the light when he asked with a tremor in his voice, ''Mommy, will you sleep with me tonight?''

His mother smiled and gave him a reassuring hug. ''I can't dear,'' she said. ''I have to sleep in daddy's room.''

A long silence was broken at last by his little voice. ''The big sissy.''