I actually don't think I used one. When I was younger, I'd either call adult women Mrs. Surname if they were in a position of authority, or by their first name if they were parents of really close friends.
Technically, I guess the answer is probably madam or ma'am, but I don't think they get used like they do in, say, France, where kids routinely call adults monsieur and madame. I've only ever said madam or sir in a really professional letter.
By the same token, I don't think anyone really calls little girls miss or missy in the UK, whereas mademoiselle gets used a lot in France.
I know you guys in the US use missy to refer to clothing sizes for young girls.