A child safety seat assembly adapted to be mounted on a vehicle seat with a safety unit that includes a first belt provided with a catch, and a second belt provided with a buckle for engaging the catch after the first belt has been extended across said child safety seat assembly, said child safety seat assembly comprising: a seat body having a lateral side (111, 112) and a rear side; a buckle-positioning member that is disposed on said seat body and that is operable to restrain the buckle at said lateral side of said seat body to facilitate engagement between the buckle and the catch after the first belt has been extended across the seat body; characterized in that: said buckle-positioning member includes a fastening belt connected at one side to said lateral side of said seat body and at the other side to said rear side of said seat body and having an end portion, a middle section extending from said end portion, and hook-and-loop means provided on said end portion and said middle section for attachment of said end portion to said middle section for fastening the buckle to said lateral side (111, 112) of said seat body, wherein said lateral side (111, 112) of said seat body is formed with a retaining unit, said buckle-positioning member further including a connecting part (34, 44) that is removably connected with the retaining unit, and wherein said retaining unit has at least one retaining hole (313, 312), said connecting part being formed with an insert fitted removably into said retaining hole. a seat body having a lateral side (111, 112) and a rear side; a buckle-positioning member that is disposed on said seat body and that is operable to restrain the buckle at said lateral side of said seat body to facilitate engagement between the buckle and the catch after the first belt has been extended across the seat body; characterized in that: said buckle-positioning member includes a fastening belt connected at one side to said lateral side of said seat body and at the other side to said rear side of said seat body and having an end portion, a middle section extending from said end portion, and hook-and-loop means provided on said end portion and said middle section for attachment of said end portion to said middle section for fastening the buckle to said lateral side (111, 112) of said seat body, wherein said lateral side (111, 112) of said seat body is formed with a retaining unit, said buckle-positioning member further including a connecting part (34, 44) that is removably connected with the retaining unit, and wherein said retaining unit has at least one retaining hole (313, 312), said connecting part being formed with an insert fitted removably into said retaining hole. said buckle-positioning member includes a fastening belt connected at one side to said lateral side of said seat body and at the other side to said rear side of said seat body and having an end portion, a middle section extending from said end portion, and hook-and-loop means provided on said end portion and said middle section for attachment of said end portion to said middle section for fastening the buckle to said lateral side (111, 112) of said seat body, wherein said lateral side (111, 112) of said seat body is formed with a retaining unit, said buckle-positioning member further including a connecting part (34, 44) that is removably connected with the retaining unit, and wherein said retaining unit has at least one retaining hole (313, 312), said connecting part being formed with an insert fitted removably into said retaining hole.