>"I want my subject [moving children] to be
clear and in focus. ... while making the background
This effect (bokeh) is most commonly achieved through the use of a fast/bright (large aperture) lens (f/2.0-ish) on a large-ish sensor (4/3, APS-C or above). Although the distance to the subject and the focal length also factor into it.
>"I've seen other photos of water where the water looked blurry but the rocks and things in perfect focus."
This is usually a different effect achieved through the use of a slow shutter speed (and possibly a neutral density filter for proper exposure). It's possible to use a different technique because, unlike the children in the previous situation, the rocks here aren't moving.
HTH - Mark
I'm a mom of four busy kids. So I frequently take pictures of moving children. I want my subject to be clear and in focus. How can I do this while making the background blurry?
I took some great pics today of my children in front of a waterfall. I've seen other photos of water where the water looked blurry but the rocks and things in perfect focus. I was hoping to achieve this affect with my child in the foreground.
Any suggestions for creative pictures of children?