Adaptable seat for vehicles

The seat (10) comprises a vertical back (11) and a seat part comprising a horizontal cushion (14) and a seat nose (16) at the front free end of the cushion. The seat nose has the shape of a triangular prism with its upper lateral face corresponding to the extension of the cushion seat surface. The seat nose can occupy an adult position where the length of the seat part is a maximum and a child position where the seat part length is a minimum.