After nursing from mommy for awhile you start to share some, "inappropriate" truths with your Mom. At least she feels they're inappropriate for a boy of your age. Trying to reach you hand underneath mommy's dress and feel her. Admitting you'd like to have sex, ... with your mom. Eventually allowing your hand to please her, and in her aroused state she decides to play with your cock and eventually inviting you to get on top of her and fuck mommy just the way you've been wanting to.