How to scare a child and yourself. 

Step 1: Grow a beard.

Step 2: Grow old . . . approximately twenty years older than said child.

Step 3:  Contemplate some general unfairness of life that you realized during twenty years you were waiting to grow old, such as why people die, having to work for a living, or why adults can't wear pajamas with feet and a big zipper in polite society.

Step 4: Whisper said truths in child's ear, then make a large clapping sound in the child's other ear.

 Step 5:  Double check child is crying.  If not, repeat until desired effect is reached.

Step 6:  Feel horrible about yourself and what you've become.

Step: 7:   Resolve to get younger, never die, quit work, and buy new pajamas.