I don't take my daycare kids in the car but if I was, just do it one by one with your car in the garage. Once they are buckled in, in a locked garage ...they are only waiting a few moments before you come out with the next.
I just started up my daycare again after moving cities and I have all young ones. You just take it one step at a time. LOL bugaboo- I have an assembly line too as mine are all in diapers
We go out for walks all the time and I have a Step two Choo Choo and they are all strapped in and away we go. I have our Choo Choo in the garage and just take one at a time and then when back from our walk, take them in one by one. They are in a locked garage for just a few moments before I come back to get them one by one and I've never had any of them get upset. My daycare parents are aware of it and also fine with it.

have fun on your new venture! It's a rewarding job- just don't sweat the small stuff but as kidlove says; prepare to sweat !!!