pretend

I think pretend friends are good. I had one and so did my son but I know a child who got a bit out of hand with it and the pretend friend became a tyranny really, to the extent that child needed the pretend friend to have meals, birthday party, the lot or he got terribly upset.
my parents took the way with me that a special friend that only I could see does not need a real chair, he/she needs a special chair that only I can see etc. This is a good way, because you do not enter into a debate about whether the friend is real or not and nor are you acknowledging the friend as real.

I did that with my son too and it meant his friend had everything in his imagination and there were no meltdowns. the first couple of times were a bit tough and i had to say that i knew this because i had a special friend that no one could see when i was young. This was true for me but maybe you will have to say someone who knows a lot about special friends told you, so that you are not telling lies to your child.