This is one of my favorites and comes from France so I give the girls names.

The Gift of the Mermaid,    Celtic, Brittany, retold by Ruth Stotter as

written in, The Golden Axe, 1998 :Stotter Press, California

    A long time ago, mermaids would rise from the waves on the Breton shores.

They were often seen on the moonlit nights combing their long hair, and

occasionally they would come ashore in daylight and spread on the sand

beautiful white linens covered with precious treasures---pearl necklaces,

rings of all kinds, and jewels.  It was believed that they found these

treasured from sunken ships on the ocean floor.  If anyone approached them,

they would wrap up the treasure in their white linen cloths and quickly dive

into the sea.

    One day two young girls were walking along the beach gathering shells.

They were surprised and excited to see a mermaid so busy playing with her

treasure that she did not notice the two girls.  They tiptoed toward her..

When they were right in front of her, she looked up, but she did not grab her

treasure and plunge into the sea.  She smiled at the two girls and said, "I

would like to give you each a present."  Then. she quickly put something in

each of two small white linen cloths and handed one to each girl. "This is my

gift. Put it in your pocket and be sure not to open it until you are home

with your parents."

    The two girls thanked her.  Then she said, "Now go to your family, and

remember, do not open your gift until you are in your home."  The girls ran

off. When they turned to look back, the mermaid waved and dove into the sea.

    One of the girls said, "Why wait until we are home? I want to see the

treasure the mermaid gave me."

    But the second girl said, "She told us to wait until we were home with

our parents."

    "I don't care," said the first girl, and she sat on a rock and opened

her bundle.  But inside there was only dirt.  "Throw your bundle away," she

said to her friend. "It was only a trick.  There is only dirt inside."

    But the other little girl took her bundle home.  her family watched as

she opened it.  It was filled with sparkling jewels!