Cut the top end of a 12-by-18-by-6-inch cardboard box.
Measure 1 inch down from the top of the box on each side; draw a line across the box at this point. Draw a line across the box that is 3 inches from the bottom across each of the sides. Draw a line inward 4 inches from the right and left edges of each side of the box; do not do this with the bottom of the box.
Use a box cutter or scissors to cut a rectangle from each side using the lines you have drawn as the outlines. Push out the cut-out rectangles and discard these.
Flip the box over so you are looking at the base.
Position the top end of a cereal box on each of the shorter sides of the bottom of the cardboard box. Move these so they are lined up in the center of the sides of the box but flush along the outer sides. Use hot glue to attach these cereal boxes to the cardboard box for the legs of the crib.
Paint the cardboard box and cereal boxes white with spray paint. Let them dry.
Flip the crib over so it is sitting on the legs to begin playing.