I agree with Mickyc, I learned pretty quickly in doing this that the more you "entertain" even program for the kids the more they expect it. When I first started I did all kinds of stuff and the kids struggled with free play. I stepped back majorly and the kids have developed fantastic imaginations and skill sets. That being said, sometimes cold turkey does not always work well especially if this child is struggling with anxiety. I would take a step back for sure and I would set up certain times when you are free that they have to do indiv play. This way you can help coach him but he develops the skills. He can have a special "box" of activities he can access during this time so he looks forward to the indiv play time. I would also let the parents know that he is struggling with this and ask them to support you at home by allowing him to play on his own at times. The I would leave him to figure it out without your involvement.