How do you deal with anger or disagreement? Are you able to express your feelings of anger directly to the person involved about the issue that really causes it? Do you then work at resolving the conflict?
It is through watching and listening to you that your children will learn much about how to relate and express themselves. They can learn from you that it is okay to express anger, even towards those they love. They will still love and be loved. They will learn to say directly, "I feel angry when..." to the person who occasions it.
If children learn to appropriately let others know their anger, they will have no need to express the emotion indirectly to others in pent up outbursts, in poor school work, etc. Nor is it so likely to be done in put-down terms or by fighting.
Parents do need to spell out certain ways of acting. Parents can make themselves available for listening and talking with their children. A firm statement of expectation made at times of quiet discussion serve children well. At the height of a fight is no time to remind children of expectations, but when all have become cooler is time for a reminder. These expectations are best expressed in terms of the parents' feeling the need for, rather than, an authoritarian directive. For an example, one might say "As we talked about the other day, it hurts me when others are hit. So I want to remind you not to hit your sister when you are angry."
This can be another opening to talk about ways to deal with angry feelings. Feelings can also be looked at separately from the action that has triggered them. At this time, alternative solutions can be opened up.