Maybe the car could be designed to split in half lengthwise
Put two concept bikes side-by-side, attached by some kind of linkage, if you need an extra seat. People should have to have their own vehicle, otherwise they are fostering dependence on someone else, and at the same time burdening someone else with extra costs. Steering and throttling might be mated electronically. Even if you have to pull a trailer with the kids in it, communication might be easy with an intercom.