It's not easy for parents to know what to do for a child who's feeling stressed.
Here are a some ideals:
Notice out loud. Tell your child when you notice that something's bothering him or her. Name the feeling you think your child is experiencing. ("It seems like you're still mad about what happened at the playground.") This shouldn't sound like an accusation (as in, "OK, what happened now? Are you still mad about that?") or put a child on the spot. It's just a casual observation that you're interested in hearing more about your child's concern. Be sympathetic and show you care and want to understand.
Listen to your child. Ask your child to tell you what's wrong. Listen attentively and calmly — with interest, patience, openness, and caring. Avoid the urge to judge, blame, lecture, or say what you think your child should have done instead. The idea is to let your child's concerns (and feelings) be heard. Try to get the whole story by asking questions like "And then what happened?" Take your time. And let your child take his or her time, too.
Comment briefly on the feelings you think your child was experiencing. For example, you might say "That must have been upsetting," "No wonder you felt mad when they wouldn't let you in the game," or "That must have seemed unfair to you." Doing this shows that you understand what your child felt, why, and that you care. Feeling understood and listened to helps your child feel supported by you, and that is especially important in times of stress.
Put a label on it. Many kids do not yet have words for their feelings. If your child seems angry or frustrated, use those words to help him or her learn to identify the emotions by name. Putting feelings into words helps kids communicate and develop emotional awareness. Kids who can do so are less likely to reach the behavioral boiling point where strong emotions get shown, through behaviors rather than communicated with words.