Select a paper bag of any size. The bottom of the bag will be the top of the pinata.
Use markers, stickers, streamers, and cut paper to decorate the bag. Don't decorate within a few inches of the open end.
At the top of the pinata, poke two holes on opposite sides. Add reinforcement rings. To make a hanger, thread a 2- or 3-foot long string through one hole and out the other. Knot the ends together.
Fill the bag with treats and small toys. Use crumpled paper as filler.
Close the open end of the bag, fold it down a few times, and staple it.
With an adult's permission, hang your pinata, have some blindfold you, and swing at the pinata with a plastic bat. Take turns with everyone until the pinata breaks, then share the treats and toys.