She wanted to tach her new daughter how to play and please her.  Her husband had left long ago.  Lacking sexual intimacy in her life she began to teach her little sissy son how to please her.  They embraced tightly and she could feel getting harder and pressing into her thigh.  She was getting excited and reached into his pretty little frilly panties to feel his growing cock.  He jumped when she first touched his clitty and looked her in the eyes.  "Does that feel good, my little sweet one?"  "Yes, it does" he moaned.  She stroked hard trying to see how big his cock would get.  This was her first time seeing him fully erect and hard.  Soon she would have him licking and sniffing her panties.  He would always crave her panties from then on