I cannot speak to black culture, but some of my friends who don't have kids are called "auntie" as a term of endearment. Not so much now that my kids are grown, but when they were younger. Most people like to indulge cute young children and like being given an honorary title. Most of the time, when I'd have an outing with a friend and my then-small kids, it would be a female friend, so "auntie Lori" or whatever would be the term used.