Figure out which leads connect to the positive (+) side of the battery. Usually these are the longer ones (see picture below). Kids can have fun trying out the LEDs with the battery directly.
Push the LEDs into the holes so that the positive leads are on the outside and the negative leads are next to each other in the center.
Bend the positive leads down through the channel into the bottom of the battery cutout.
Push the battery into the cutout with the positive (+) side facing down.
Twist the negative leads together and bend them down so they hover over the battery. When they are pushed onto the battery, the eyes should light up.