Upvote:6
You cannot drive to the Jungfraujoch. The closest train station to the Jungfraujoch that has parking facilities is Grindelwald Grund.
Upvote:8
Ticket for the Jungfraujoch you best buy from the railway itself. Do not get an third party involved. Especially one that makes incorrect claims like "likely to sell out". You should never buy a ticket for a mountain excursions till you know the weather, and in that area that means not more than 24 hours in advance.
The best thing to do in your case is to leave your car at your accommodation (or even better, not bring your car to Switzerland at all) and just walk or take the bus or train to Grindelwald Terminal, where the Eiger Express cable car brings you to the Eigergletscher station and from there by train to the Jungfraujoch. Ticket prices you can see at www.jungfrau.ch.
This ticket is only free for children if you have a Swiss Travel pass. The "getyourguid" website does not make this clear, setting you up for an expensive surprise...
You car will probably spend the entirety of your stay in the area parked, as all the interesting excursions are not car accessible.