This is certainly not a direct solution, but it can be helpful. Remember, sometimes children have a hard time even figuring out what makes them sad. In those cases, doing something they like may make them feel better and it can give you a chance to talk.
But even if you do decide to do something fun to distract your child from their sadness, you should always use it as a chance to talk. Once they start to work through their feelings of sadness or distress, they may be able to step back and put into words what was bothering them and why.