For pictures of children and pets, or portrait photographs in general, many of the cameras on the market today are extremely capable - portraits are simply a category of photography that depends mostly on your own photographic creativity and has little to do with the features or performance of the camera.

The most important feature here is having a moderately long zoom range that will produce more flattering pictures than a wide-angle lens. The Casio V7 covers this range well, and the Olympus 820 is adequate as well, although the F40fd has a more ordinary 36-108mm range.

For shutter lag, the Casio V7 is the quickest and most responsive camera, and the Fuji F40fd is a decent performer too. The Olympus 820 has below average performance, which may make it difficult if you plan to take mostly candid pictures, or if your children or pets are very active and don’t sit still and pose very well. It’s important to note that there aren’t any standardized tests for shutter lag, so gaugeing performance is often difficult and even subjective to an extent - “unusably slow” to one user may be “fast enough” for another. The best thing to do may be to visit a store to try the cameras out, and see if the camera performs fast enough or too slow for you.

The third feature, important if you plan on taking pictures indoors or at night a lot (i.e. low-light situations), is having a good high ISO capability that can prevent blurry photos due to motion blur. For this purpose, the Fuji F40fd is really the only camera that performs well - the Olympus 820 will produce photos that are too blurry at the lower ISOs, or too noisy at the higher ISOs, and the Casio V7 is simply unusable outside of daylight situations.

In good lighting, where high ISO isn’t a concern, the Olympus 820 makes a solid choice, providing the zoom range needed, with a decent high ISO capability if you ever venture into lower light situations. Its only drawback is the somewhat slow shutter lag that may be too slow to capture precisely timed candid shots or active children and pets. If you try out the Olympus 820 at a store and find it to be simply too slow, the Casio V7 is also a good option that covers the portrait zoom range and responds very quickly, although its poor high ISO quality makes it very difficult to take pictures in anything but good daylight.

If you’re planning to take many photos in low-light, however, high ISO performance is essential - other features or image aspects won’t matter if the subject matter is simply too blurry. Here the F40fd is the best choice, as more or less the only camera that is capable of good results indoors without using a flash.