I could see the outline of her fingers moving gently up and down on her sister; the sister who had suddenly gone quiet, laid back with her eyes closed and a smile on her face, interspersed with the odd frown of pleasure. I leaned back slightly, opening my thighs a tad wider allowing my cock even more freedom to move and expand, whilst continuing to observe the scene before me. It was a full blooded response to a woman I was suffering, not my expected response to children.