One way to think of emotional regulation is as if a person had an emotional thermostat. It's almost as if our emotions have a certain set point and we all seem to be set at a different level. If we were air condition units, some of us might be set at 70, some at 74, and some at 78. We're all different so it only makes sense that our set points would be at different.
To continue the analogy, for an air conditioner, many factors add up before the temperature goes above a critical level. Is it 100 degrees outside? Are there 20 people in the house? How much insulation is there in the walls? Are all the doors and windows open? An air conditioner thermostat adds all of these things together and it goes off when it goes over the limit.
Your child's emotional thermostat operates in a similar manner, many factors add up before his stress rises above a critical level. What's happening at school? Are Mom and Dad fighting? How are his friends treating him? What ways do he know to cope with this stress? If too many stressors are around, they overwhelm the emotional set point and your child's emotions ignite.
The example can apply to any emotion. Anger, sadness, or anxiety. Once the number of stressors go over that level, anger explodes to rage, sadness falls into tears, anxiety spirals into panice.
Biologically, where our thermostats are initially set can be inherited from our parents. Our temperment, naturally shy or outgoing can come from our parents. Look and see, what parts of your child's personality comes from their father, what part from their mother?
Working to keep your child at an even emotional balance is a main goal for parents. Different coping skills are important to lighten the load or relieve stress. Physical exercise adn good nutrition can effect a child's internal state. At times, medication might be needed to help raise the biologic thermostat to a higher level.
Get a sense for your child's thermostat. They all have one. Learn to recognize when stresses are starting to overwhelm that level. It's a natural occurence, be prepared for it.