Pigg#1 really likes the ‘knight in shining armor’ kind of play.  But the real reason I decided to make him a crown was so he could play ‘king and queen’ or ‘prince and princess’ with Pigg#2.  
I started out by cutting out the crown with a length equal to the circumference of his head plus an inch.  That was 21 inches.  Then I cut the top triangles out.  This first pictures is of the princess one where I cut the middle point bigger than the other ones.

 Then I cut a rectangle that would cover all of the crown and sewed the crown to it.  I put diamonds in the points to be jewels.  Cut along the edge of the crown to have a double thickness crown.
 Don’t sew the ends of the crown so you can slip elastic in between the two layers and sew it in.
 So when you put it on your head, the elastic lets the crown stretch, but snug on your child’s head.
 See how the elastic stretches?
 King and Queen ready to hold court!