The youngest I was would be about 11, but it is very common for little girls to rub against stuffed animals and the like, as young as 3, 4, etc.

It's never too young to masturbate and it cannot cause harm! It will not hurt her physically or psychologically.

manually? right?

It doesn't matter. Using running bath water, a washcloth, a beloved stuffed animal, a pillow... pretty much everything is normal, including simply using the fingers.

my niece it looked like she did in the womb...we joke about it but her hands always seem to be their in ultra-sound pictures! She still does it sometimes in bed. As long as she isn't doing it in public places you have nothing to worry about, its natural.

Little girls will touch and rub before they even know what it is. Nothing to worry about.