Take one plate and cut it into half down the middle. Then take 1 of those halves and cut it into half. You have now created the tail and fins and shown in the picture.
Allow your child to paint each section including the 2nd (uncut) plate.
Finish off by cutting a small mouth out of the whole plate as shown.
Glue all the pieces together and decorate with glitter, sequins and other embellishments.