Get a clip of some kind (a simple clothespin or large binder clip will work) and every week write a new Bible verse on an index card. Write it so that it's easy to read and clip it to the visor in the car or put it in the glove box. Whenever you take a ride pull the verse off the clip and have the kids say it a few times while you ride. Be sure to keep the cards in the car and go back to old ones on occasion. The more you do that the further into the memory the verses will be stored.