A rocking device with a seat unit such as a chair, crib or cot, or attachment mechanisms for same with a motion generator comprising a profiled track defining a closed undulating path and a track follower, to interact with the track whilst one or other is rotated, thereby creating relative displacement between the seat unit and a base unit to simulate the motion of a vehicle. The device has mechanisms to decouple the relative displacement between the seat and the base from any rotational movement of the chair. The device is particularly effective at inducing sleep and restfulness in children. The invention also includes profiled tracks, and method for producing them from recording motion experienced by passengers in moving vehicles.