The kids did a great job and almost beat me. (I was a little worried that I wasn't going to win.) My shape is the long blue one and won by about 6 inches.
So, here's the trick to beating your kids. First, fold your paper in half. Notice how the first and last cuts are made. Those are the 2 most important cuts. You will go back and forth the entire length of the fold. The closer you make these cuts, the longer/larger your shape will be.
Next, you will cut the fold. DO NOT CUT THE FIRST OR LAST FOLDS. Open it up slowly so you don't rip it. It will easily be over 10-12 feet long.
I have also used this trick to challenge my kids to make a shape large enough for a person to walk through. They always think it is impossible and love to learn how to make 1 piece of paper stretch so much. I usually have 1-2 students go home and try this bet with their families!