I don't know if everyone has heard of relationship expert, Isadora Alman. She published a book in 1991 called, Ask Isadora. Chapter 5, in her book is titled, Fantasy and Friction (Solo Sex). Here is one Q & A in this chapter that really stuck in my mind after reading the book:

QUESTION: "I babysit a little girl who is just about one year old. Like a lot of kids, she has a favorite stuffed animal she likes to sleep with. When I put her down for a nap, instead of cuddling Teddy in her arms, she lies on top of him (which can't be comfortable) and sort of humps on him with her pelvis. If I try to move the toy, she gets upset. If I leave her alone with it, she humps until her face gets red and she stiffens and quivers all over. I can't think of any other explanation than that she's masturbating to orgasm. Is that possible at her age?"

ANSWER: "Yes, and from what you describe, very probable. Orgasm is a time-honored natural method of releasing body tension before sleep. Allow her to enjoy herself. There will be time enough for her to learn the socialization rules of our culture. When she begins to play with other children, she'll find out that some pleasurable activities, like picking one's nose, are best reserved for private time."