Mom, Dad, and two kids have come to a river, and they find a boat. It is small and can only carry one adult or two kids at a time. Both kids are good rowers, but how can the whole family reach the other side of the river?

The kids row across. One comes back. An adult goes over, and the kid comes back. Both kids row across again, and one comes back. The other adult rows across and the kid comes back. Both kids row across again.