It is not unusual for sibling rivalry to happen even when there are gaps in ages. Much of the time it is considered a normal developmental stage. However, it is not common for the type of behavior that you are describing. Therefore, I would suggest that you may wish to discuss these behaviors with a professional in your area, such as a mental health or a school counselor. Also, it would be important to journal if this is an isolated event due to low impulse control (part of what we call executive functioning) or part of a host of changes in your son's behaviors.
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