I have been working as a children's fashion photographer nearly 7 years. I got into this slightly niche genre by accident after a friend pulled out of assisting a two week shoot for a large children's wear designer. After the shoot I was asked to work for them full time as their staff photographer.
I love what I do, and it holds different challenges to shooting with adults. But it's also a more relaxed way of shooting. I imagine it is a bit like wildlife photography. You do all you to prepare and set up the scene. Then you have to wait for the right moment to press the shutter. It can sometimes be a long wait but it is worth it when you get "the" shot. You can't force children to do something they don't want to do. It will literally just end in tears. You have to let them be themselves and the most you can do is suggest ideas that they might find fun or interesting.
I often do test shoots. As a photographer, I need to challenge myself and discover new ways of shooting. Otherwise you just start to repeat yourself and where is the fun in that!