Ds1 would be sick every single time we were in the car for more then 45 mins. It started when he was 15 months old. He's now 7 1/2. Ds2 has never had an issue though.
We found, for him, watching a movie or show stopped it. We used to use my laptop but finally got screens installed. Best thing ever for ds1.
We still have nausea wafers for when we go on trips and those sick bags you use in hospital but thankfully don't have to use them often. Maybe 1 trip out of 10.
We had phenergen (not sure on sp either!) recommended to us by people but we weren't keen on that idea either.
Good luck OP, I hope you find something to help your ds
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