Dean doesn't have imaginary friends, but he does have imaginary tools. Every single time we read the book Tools (one of his favorite "classics" that we own), Dean has to collect every single tool off of every page. He holds them in his hands until he can figure out where to put them. Once I had him in night shorts that didn't have pockets, and he asked me to put "not night shorts" on him so he could put his tools away.
Tonight as we were reading books before bed, he was taking the shapes out of one of his library books, and what did we notice Walter doing? Picking off all the shapes off the pages! He loves Dean and watches him so much. It was funny to see him taking imaginary tools and shapes just like Dean.