The parents will try to shelter the young birds as much as possible. A parking lot is not the best area, so if you can shelter them from cars or harass them enough to leave that area (as long as there are safer areas), then it would help them seek shelter in more of a wetland habitat instead of an asphalt residence.

However, they may just be trying to reach higher ground and get the cygnets out of the water to help them dry so that they don't drown. If the parking lot can be blocked so that cars can't access that area, that would also be another alternative. The major emphasis is to provide an area out of the water as the young birds can drown since their feathers are not yet water repellent. The mother will also carry them on her back under her wings to help them stay warm and dry. Waterfowl are used to heavy rains, so this should not be a problem as long as the parents are paying attention to the needs of the cygnets. The Regal Swan