4 drops Peppermint
4 drops Ginger Root
9.5 drops Carrier oil of your choice
Add the essential oils to a 10 ml roller bottle, fill the rest of the bottle with carrier oil and shake to blend.
Apply the oil just before you get in the car and if you're taking a long trip, reapply as needed. I like to apply it to the stomach and to the pressure points for nausea on the inside of the wrists. There are instructions on how to find the pressure points at https://exploreim.ucla.edu/self-care/acupressure-point-p6/
My son prefers to use an inhaler so that, in his words, he doesn't end up "smelling all herbal". He resisted using essential oils at all at first, but they worked so well that now he won't go on a car trip without them. I use 7 drops of each oil in his inhaler.
My kids are old enough to use peppermint without any concerns, but if you want to make a blend for a young child, be aware that peppermint oil shouldn't be used on or near the face of young children. You could try using spearmint instead of peppermint - I haven't tried this myself but spearmint is also meant to be effective for nausea and is safe for young children.