There is not a way to get to Arenal without some twisty driving even if you fly to Liberia. If the meds don't work out I would reconsider that part of the itinerary.

Thanks for all the advice - I really appreciate it.

I also have a child who was very prone to motion sickness. We used dramamine and sea bands in Costa Rica. The only time we had a problem in CR was on the public bus. I think that was the heat and the exhaust smell.

I believe that the ingredient in the longer acting nondrowsy dramamine is the same as in bonine. At 15 my child has outgrown the worst of his motion sickness. He can now ride in the car on the highway for several hours without a problem. I would still give him dramamine if we were going through mountains

Just to follow up on this thread, in case people are researching this issue. I looked into it and there is a children's Bonine that has a different active ingredient than regular Bonine; regular Bonine is not recommended for children under 12. I have looked in a number of my local pharmacies and have not been able to find the children's Bonine, but it is available online at drugstore.com. I'm going to keep looking because the shipping is more than the box of pills! Ginger candy is another remedy for motion sickness, apparently. Many cruise forum boards talk about it and how it works for both kids and adults. We'll probably try both these remedies before we head to Costa Rica. Thanks for your help, everyone!

Just to follow up on this, we ended up ordering children's chewable Bonine tablets online and using that on our trip to Costa Rica. We drove on many bumpy, curvy roads and did not have one incident of carsickness. Each time we had a travel day, I would give my kids one with breakfast and it worked like a charm. My eight-year-old even said, "Wow, that stuff really works!" I highly recommend it.