If you search for a particular reason, such as his father's
travelsTravel sickness, to explain your son's aggressive behavior, your search will likely be in vain. Such children behave in a disorganized, aggressive fashion usually for one (or both) of two reasons. One is that, in the presence of groups, children who are immature developmentally tend to feel vulnerable, unsettled, and when this occurs they become aggressive. The other reason is that, when such children's wishes/wants are interrupted, they become angry and strike out. My sense is that you are witnessing both phenomena. The recommended strategy is to implement a very structured, systematic plan to manage the behavior. Usually such plans have two facets: one involves rewards for acting safely, the other involves strict, clear limits on aggression and periods of immediate time out for any transgressions.