Under the Sea ...

where mermaids and mermen live. 

We learned how make tails without sewing. Karen's is a costume, but the others are homemade.  We found the instructions on YouTube:
stretchy pants and pillow case are the main parts.  1. Put on swimming suit, 2. Put legs in one side of pants, then rap other leg around waist and tuck the end in (so you can use the pants again). 3. Place pillow case over feet and tuck under stretchy pants. 4. Pose for your picture!
For a more defined fin, use a large cardboard cut out in pillow case.
The boys were having just as much fun as the girls.