Decorate with paint or markers. Tape a piece of kite string that is about 3' long between each of the side corners. If you make a loop in the ends of the string before you tape it down, it will be stronger. Tape a piece of flag tape about 5' long to the bottom corners. Tie multiple square knots so it will hold.
All products are available at craft, hardware, and grocery stores.
Tie the 3' and 2' dowels in the shape of a cross. Use a craft knife to cut a notch in both ends of each dowel. Thread kite string around the frame so that the string rests in each notch, and tie off. Lay the diamond-shaped frame on top of the plastic bag and trace the outline. This is the body of the kite.