Taking kids by surprise with change is, I would say, the main cause of tantrums, along with hunger and tiredness. So, in order to have to deal with less sadness, I usually give five minute warnings for things like: going to bed, leaving someone's house, going on an outing, stopping their computer time or t.v. time, sharing toys, eating dinner, and any change in activity. I say something like, "Ray, you have five minutes before your friend has to go home." And magically, this makes it all okay. Sometimes I give a two minute and one minute warning if I think it's going to make them really sad, and if they are really young. So try 5 minute warnings if you haven't already. You'll find it reduces many of the tantrums at your house!