Very often when a child expresses strong emotions such as anger or sadness, parents are quick to avoid or discount the emotion. Ironically, most parents I work with have a fairly good sense of what might be upsetting to their child.
The next time you encounter strong emotions from your child, resist the urge to stop the emotion. Instead, offer up possible reasons for their upset. This is especially helpful for younger children that may not yet have the capability to verbalize these strong emotions. It is helpful to comment on what is observable with your child and offer tentative possibilities of what might be upsetting them.
For example, "Boy,you look really mad. I can see your fists clenched and your eyebrows scrunched. I am wondering if you are mad about......"
The key to this is to not always feel you have to guess the real reason your child is upset. It is more important to be present with your child's emotion, rather than avoid it. Almost always, this helps reduce the intensity the emotion rather than increase it. It is often when a parent avoids or discount the emotion that child's behavior begins to escalate.