Ducklings cannot fly. They will all hatch on the same day and the hen will walk them to a nearby source of water. In urban areas they sometimes have quite a walk, but they usually make it just fine. You should not try to move the ducklings. They will scatter when you approach which may cause them to get separated from the hen. Ducklings move pretty quickly, so they should get across the street o.k. as long as it isn't a major highway. Hopefully drivers that see them will stop to let them get across. They are protected by the Migratory Bird Treaty Act, so it is illegal to intentionally run them over with a vehicle. It is great that you are concerned for them, but don't put yourself in harm's way to help them.