My baby just started preschool too, a couple weeks ago, in the SN classroom at the public elementary school. For now, I am going with him as his aide. I think he is ready for me not to be there, but there are not enough support staff in the classroom right now. He's a runner too, and their outside play time is right next to a hall that leads into the parking lot. He also needs help with sitting through circle time, and with transitions. I am working on getting him a one-on-one aide, but it takes paperwork, many days of observation, and another IEP meeting. I hope it goes through soon, I start a new full-time job at the beginning of September, so I won't be able to go with him after that.
But, he's doing well, he likes it much better than I thought he would!