There are two (learning) steps to this activity. The first step is the fine motor work of cutting up the pipe cleaners. This can be a hard and frustrating job for little ones because of the wire in the pipe cleaners, so it's better for older ones with more hand strength to do for the younger ones.
Next, place all of the cut up pipe cleaner pieces into a glass jar. Give each child a magnet and let them explore with moving the magnet on the outside of the glass and then inside the glass. Talk about WHY the pipe cleaner pieces are moving and then move the activity to all over the house by exploring what else is magnetic. DON'T ALLOW MAGNETS NEAR ELECTRONICS OF ANY KIND.