OH THANK GOD. There's a book for that!
Flexible integration.
As a small tot I had an imaginary friend named Shadow. No joke. I can only imagine what Joseph Campbell and Carl Jung would have to say about this. Shadow was a shaggy black-and-speckled 70's bathmat type of thingy. If it was a holiday and we had company over, I would drape him over my little arm and show him off, but with a shyness. 'Do you want to pet Shadow?'. My parents let me pick out a kitten soon after this phase.
Shadow met his demise somewhere around my 3rd year on earth; my brother threw up on him during a nasty bout of childhood flu.