DS is nearly 5 and has recently announced the arrival of his two "magical friends", France and Mad. He talks to them and does voices and everything. He even made me talk to one of them the other day 
I don't have a problem with him having imaginary friends, I think it's quite sweet and I'm sure it's a good sign as far as his imagination goes, but it does make me wonder if he's lonely. He's an only child who really seems to thrive on the company of others and I often feel hugely guilty that he doesn't have any siblings, especially as I find it difficult and tedious to play with him as another child would. Due to our situation currently, DP and I are not planning to TTC for another 1-2 years, and even then we don't know how long it will take or if it will happen. I feel really sad for DS!