Measure the largest piece of art you want to keep. Cut two pieces of cardboard at least 2 inches taller and 2 inches wider than this artwork.
Ask your child to paint the cardboard, which will form the outer layers of the portfolio, much like the cover of a book. Allow it to dry completely.
Line the two pieces of cardboard up as if they were attached into the final portfolio. Cut small, dime-sized holes down the binding edge of both pieces of cardboard, about 1/2 inch away from the edge. Make sure the holes in both pieces line up with each other.
Weave the ribbon through the holes, starting at the top, traveling all the way down the binding edge, and finishing back up at the top. Tie the ribbon in a bow and cut any excess. Place artwork in the portfolio.