The two best developers I ever hired, I hired as interns. When I became a manager I started discussions with our local college and attended their career days to recruit juniors and seniors. I was lucky enough to land several people, all of whom were eventual contributors. Two of them became senior developers and were core to the success of our team.

It's cynical to think that every developer you hire without experience is going to leave after a year. As you mentioned, that's a product of a lack of mentoring and incentivizing retention. Reward effort and progress toward career goals, not solely their individual accomplishments that further corporate goals and you will retain them. Manage them as people you care to work alongside, not as a "report" and you will end up with a stronger team.