John Patrick Thomas

Assure that your son initially sits in the front seat. Have him avoid looking at any form of screens or print material. Avoid travelling after he eats and assure that he is well hydrated. Important that the driver avoid certain forms of terrain such as excessive curves, any form of a 'roller coaster terrain', roads that have significant variance of car speeds. Having accomplished all these features, when riding have your son focus on a distant structure.
Trust these interventions will help, but have a small emesis basin available, clean immediately and use deodorizers to refeshen the car environment before continuing if he does happen to vomit.

I would see little need to have preemptive consultation with a psychiatrist for your asymptomatic daughter. Look to assuring an open relationship between your daughter and yourself as well as her father. Establish an open door policy for her to address any issues she is concerned about.

Probably of equal importance, assure that your daughter is establishing strong relationships with very stable friends, the number of friends isn't as critical as the quality of friends. Be optimistic about your daughter.

More information is desirable about this infant's development to comment. In comparison our son walked at 9 months and our oldest daughter at 15 months and later graduated magna cum laude both from college and graduate school.