Abstract: An infant's or small child's protective seat constructed for securement to a snowmobile, motorcycle, or similar vehicle has a rigid and structurally strong, body-receiving seat structure preferably integrally formed with upstanding back wall and side walls for enclosing substantially the entire body of the occupant in seated position, and has a transparent, bubble-type hood hingedly connected to the upper part of the back wall for seating upon the side walls when in closed position and for swinging backwardly into open position to permit entry to and exit from the seat. A body-restraining harness is anchored to the seat structure for holding the occupant firmly in the seat, and means are provided for latching the hood in its closed position. Means are also provided for detachably securing the seat structure to the vehicle in superimposed position on the vehicle's seat.