Hi B., I have seen this often, I use to be the head of the Nursery long ago, this is my suggestion, stay in the room with him for maybe the first month, each time maybe start to leave after being there for half the service, its like anything weening a child from a bottle or pacifier, you don't just take it away all at once, stay active with him, and watch his interaction with the other children, this is a very attached age, and a time where they start showing a clingingness around strangers, he doesn't know anyone so you must stay introduce the little one to everything, better you then the nursery worker that he doesn't know either, and I'm sure they will not have a problem with you staying they can use your help, you will have a much happier child in the end.