Doing it often so they don’t lose the habit 😅. But also make sure they’re fed, near their nap time, have something to drink in the car. Make sure to give them their blankies/binky/stuffy whatever they take in their crib.
Always around nap time works for us
We make sure to time it for nap time and play the same white noise we use in her room over the car speakers until she falls asleep. We also had our back windows tinted because we noticed the sun bothers her eyes.
I have not seen anyone mention the following: WEAR YOUR KID OUT! If we are going for a long car ride I make sure that kiddo has had a ton of activity so when we get in the car they are tired and want to sleep. Full belly as many mentioned and for us, a paci
We make sure she's full and close to her nap time does it every time