Imaginary friends come in all shapes and sizes. They can be based on someone your child knows, a storybook character, a cuddly soft toy or can come entirely from your child's imagination.
You may find yourself having to set a place at the dinner table for coco the purple monkey or having to discpline that pesky monkey for eating all the biscuits in the cookie jar! 
When do they appear and how long do they last? 

Children can have imaginary friends from as young as two and a half. They will usually stop playing with imaginary friends when they are ready to move on. Experts suggest that imaginary friends are likely to be around for several months but could be a feature in your child's life for up to three years.
Why do children have imaginary friends?
Your child’s imaginary friend could be someone who:
  • Listens to and provides support for your child
  • Plays with your child
  • Can do things that your child can't do
  • Is unique and belongs only to your child
  • Never judges or finds fault with your child
Your child has complete control over what the imaginary friend does and says. This in itself can be part of the appeal of the imaginary friend.An imaginary friend allows your child to explore a make-believe world that they have created entirely by themselves. In fact, some experts believe that children with imaginary friends may be more imaginative and more likely to enjoy magical stories and enjoy fantasy play. Make believe friends can offer great insight into your child's inner world, likes, dislikes and tastes.