After one skein worth of crocheting on the bottom section of the girl's cardigan, I decided to stop and test out the pleating. With about 6 vertical inches worth of fabric, the pleats and my imagination should tell me if I should continue with a true rectangle or start to taper as I get closer to the waist. A seven year old doesn't have a "waist" per se, but I'm improvising with what will make the garment more stylish. Generally speaking, she wears more fitted clothing now than she did when she was 4.
To make it easy on myself, I ran a contrasting yarn through the 38 inch width of fabric (which does match the pattern schematic) and gathered it up and put it around her. There was WAY too much fabric. Instead of ripping back and attempting fewer pleats until I hit the right look, I decided to turn the rectangle on its end and crocheted a starting chain that was tall enough to stretch from below the chest to the hips. With many tens of rows (I didn't count...), this grew to a rectangle that wrapped around her from belly button around and back to the belly button.
This saved me time and ensured that I end up with a rectangle that is the right size to fit around her middle without pleats. I didn't need to do any waist shaping so it is still a rectangle - just a much narrower one. Crocheting a fabric vertically instead of horizontally may also give the sweater a little more drape - I expect to know more once I connect the lace top portion.
You may be able to tell from the picture, but I also changed the stitch pattern for this rectangle. The pattern called for double crochet but since plain double crochet isn't my favorite or hers, we decided to use the double crochet/single crochet repeat that I used for my Crochet Cardigan two projects ago.