I took Quinn to a mall playground today and led him through some highly over-supervised play. I was constantly nervous that he'd hit or kick someone so I was on him like the most ridiculous helicopter mom. But it really worked surprisingly well - it was the first time I've seen him engage with other kids.
The only kids he showed any interest in were toddlers. Anytime a kid his own age would approach and try to talk to him, he would just stare blankly. I think his OT may be right - he doesn't know how to communicate with kids his age. But babies are awesome - they don't talk and he can lead them around like he's the Pied Piper. At one point he looked up at me all excited and said, "Mama, I am playing with the baby!"
He did lean on one baby too hard and made her cry, and later he grabbed a boy's foot which caused him to fall off a low play structure, but neither was as big a deal as it sounds. The first got him a time out and the second meant we had to leave. But I left feeling more encouraged than I have for a while. Despite what I thought, he does fully engage with kids - just not kids his age.