There are literally hundreds of crafts to make with your child that use cans. Pencil cups, telephones and even stilts all use tin or aluminum cans. Both types of cans can be used in crafts. Soup generally comes in tin cans, but occasionally soup is packaged in aluminum cans. To tell for sure whether the can is tin or aluminum, place a magnet against the can. Tin cans all contain some steel, so if the magnet sticks at all, the can is made from tin.
Open your cans with a safety can opener. This opener actually cuts the along the side of the can. This allows you to lift the lid off the can and leaves a smooth, safe edge that won't cut little fingers.
Feel around the edgers of the top of a can opened with a traditional can opener. If they feel sharp, sand the edges to blunt them with a heavy grit sandpaper or a steel file. Work your way around the sides of the top of the can until the entire cut edge is smooth. Carefully feel the inside of the can for any sharp portions that you may have missed. It doesn't have to look beautiful -- it just has to protect the child while she works. Depending on the craft, you can cover the edge with glued-on paper or ribbon to keep it safe.
Wash out the can with dish soap and sponge. Wipe away any soup residue or oil.
Peel the label off the outside of the can. Not only does this prepare the can for crafts, but it also removes any paper that could become a choking hazard for young children.
Check the outside of the can for glue. If the glue is soft, peel it off of the side of the can. If the glue is hard, sand the glue to make sure there are no sharp edges.