Ask the children where "Paul" is. They will probably look at you as though you are mad, but continually ask them where "Paul" is today. Tell them that he normally sits in his space (point to the empty chair) and that he was there yesterday, but he isn't there today. Insist that they tell you where he is. Hopefully someone will make up a reason why "Paul" isn't in today. Argue with them, saying that you have heard differently. Ask if anyone knows anything else. Ask who was the last person to see him. Continue like this for a while, with the children explaining where he is.