The present invention relates to a child safety seat assembly for two-wheeler vehicles, in particular Underbone (Kapcai) motorcycles. The team have prepared 2 type of designs for the safety seat. The first design is a portable or a latch-on design which can be latched and fastened securely to an existing underbone motorcycle. The second design is a permanent safety seat type design where the existing underbone motorcycle seat is removed and replaced with our safety seat.