If driving the kids to the school isn't the problem can you arrange with another parent doing the same thing to take your child to the door and bring him back out to the car at the end of the day - maybe in exchange for one of you standing between the two cars to monitor the kids inside so neither of you have to take the kids out.

Also see if there is a different way around such that if you arrived 10 minutes earlier you would have time to walk the long way around on what would be shovelled walkways and then have the toddlers walk with a stroller for the very youngest.