This mermaid tail was designed for a teenage niece, but I soon had requests from the grown-ups for them too. Requests for a version for smaller children soon followed, and the design here is suitable for children about 5-6 years of age, or older if you make the tail longer.
The Wavy pattern mimics scales perfectly and using variegated wool gives interesting colour changes

For the adult/ older teen size finished tail is approximately 40 inches (102cm) around the waist, the main tail is about 46 inches (117cm) long with fins an additional 12 inches (31cm) long.
Instructions are included for how to make the tail LONGER or SHORTER and for how to increase to a waist of approximately 50 inches (127cm) or decrease to a waist of 30 inches (76cm). If you want an even bigger waist you can easily add in more pattern repeats.
For the child size the waist is approximately 30 inches (76cm) and the tail is about 28 inches (71cm) long. Instructions are included for how to make the tail LONGER or SHORTER

• I used James C Brett marble chunky wool – but you can use any chunky (USA bulky) wool you like. You will need 2 x 200g balls for the adult tail and one ball for the child size tail
• You can use the same wool for the fins, as I did for the adult sizes shown in the pictures. Alternatively you might want to use contrasting wool for the fins. Use any chunky (USA bulky) wool or you can use 2 strands of double knitting (USA Light Worsted). For the child size version shown in the pictures I used Phildar Myridae wool (colour Nuit) 2 x 25g balls, which has a metallic look. I used 2 strands of this together on size 6mm UK size 4. USA size 10 needles.
• I used size 6.0mm circular needles UK size 4. USA size 10 for the main tail and size 6.0mm UK size 4. USA size 10 straight needles for the fins