Massage can help but it's a bit disconcerting when a 4 year old demands massages lol.
Guided imagery used to settle one of ours right down.
We give Mr 4 the celestial seasonings sleepy time tea. It's mainly camomile with some other stuff. Plain camomile is the tradition calming tea.
They used to do yoga at their childcare center. You can find kid's yoga on youtube.
A portable DVD player can lull them into a zombie like state on long journeys.