I suppose any brand on sale at a ''proper'' shop will do. However, it should not be used for archiving. All photos should be uploaded to the computer HD (and then backed up), so as to leave space for more photos. So, a 64 MB or 128 MB card is more than enough for your purpose of taking photos(low resolution, highly compressed) of children for documentation, unless you are talking of taking 100's of photos at one session.
I take a good amount of photos because we homeschool out children and tend to document everything. I was thinking I need at least 512MB of 1 GB but I am not sure. Is there anything I should be looking for exactly? Brands I should stay away from?