I would recommend reading them in order starting with The Song of the Lioness quartet (Alanna: The First Adventure, In the Hand of the Goddess, The Woman Who Rides Like a Man, Lioness Rampant). They're in the right order on the wiki page. She has two main universes, the Tortall (which is the first set) and the Circle and they're both good.

And yes, they do talk about some adult concepts, but they aren't explicit. The one I remember the most is that there is talk about periods (Alanna freaks out on her first one) and anti-pregnancy charms. And there's some how-babies-are-made talk, but not much.