UC Berkeley Extension has a Lifespan and Development course called Introduction to Developmental Psychology. It's kinda expensive... ~$600-700 but the class itself is pretty easy, just short essay response and readings. I'm currently taking it now while working full time and it's definitely doable. It's also self-paced so as long as you finish the class by the 6 month deadline from when you registered, and take at least 90 days to finish the course, you can pace yourself however you like.