Why do people call their little girls "mommy" or "mommas"?

And other variations of this nickname.

I've been hearing it more and more lately. It's usually the moms that call their daughters this.

It makes me cringe a little every time I hear it, but I'm genuinely curious why people call their little girls this. Like, to me, these nicknames refer to a mother, someone with children. So why call a small child these names?