Book where a woman discovers an object that turns into a boy

My wife cant remember a book she believes she read before 2015. She thinks it might be a YA fantasy book. So a woman finds some magical object in a cave or something and she hides it. And a Goddess sends someone to protect this object. She thinks his name might be Jack. Also there are others (bad guys?) trying to find it and they can use magic. Later this object magically evolves in to a boy with magic powers too