Magnetic number fishing, they add what they catch! As well as addition, develops hand/eye coordination, fine motor--I love this for magnetic letter fishing too! When they catch a letter, they say its name and sound.
MIGHT USE THIS IDEA - Very Hungry Caterpillar Mobile. Hang lanterns red, 6 in two shades of green) with different lengths of fishing line. Use pipe cleaners for antennae, and construction paper for eyes and nose. Very cool in a children's library space.