Paul Buckhiester wrote:
I have learned, the hard way, not to scrimp on shutter speed with moving people, especially kids. Also, shallow depth of field is not our friend in candids.
So, low light performance becomes the solution. Add some good glass and skilled focusing and —- success!
For people photography in general shallow depth-of-field is very important and useful in isolating your subject as in child portrait photography which is the subject here. For just general, out in the backyard, work, a bit more depth can produce better images. Shutter speed, especially with quick moving children, is also important as stated. Best of luck.