You should start by visiting this site, http://www.professionalchildphotographer.com/ by Marianne Drenthe/Marmalade Photography. It is an indepth guide to professional portraiture and a great guide for clients teetering the decision to contract a pro.
Below are 2 examples of before and after images. These were taken of my Natalie late one night at 1130pm. She was very tired but restless. Would you believe it took me nearly 40 minutes to get her in the pose I wanted (1st image) completely asleep before I could even touch my camera? 40 minutes!! The second pose was much easier as she had been asleep for a good 20-30 minutes and thankfully stayed asleep.
You can see the before (SOOC = straight out of camera) with a simple exposure bump and I adjusted the white balance. And then you can see the after. I spent about 15 minutes processing each of these images… NOW… multiply that by 30-60 images, and I’m sure you can understand why professional photographers charge as much as we do. These images, your images are art. They are your memories, and it’s my job, my craft, skill and knowledge to make them for you. Any reputable photographer will not just give away their art, their hard work.
Again, please visit Marianne’s informative site. You’ll come back with a slew of new knowledge… and knowledge is power! 
