Aside from the above suggestions (which are all awesome!) and dealing with the underlying causes, here is an idea I have. In the preschool where my SO works, the kids "push" their parents out the door. Every morning they give a hug and a kiss, and then the kids have fun pushing them out the door. It gives the kids a sense of participation and power in the seperation, and it is something that makes them laugh as they begin the day at school. Done everyday, this seems to help some kids some of the time when nothing else works.
I'm pro-adoption reform, but not anti-adoption.