Car seat for a child, intended for being secured to the seat of a motor vehicle

The invention concerns a child seat intended to be installed in a vehicle, in particular an automobile, equipped with a safety harness intended to keep a child seated in the seat, comprising two shoulder straps (13 1, 13 2) and a crotch strap (14), a release means (16) of said harness being provided, in the vicinity of said crotch strap (14), in an opening made in the surface of said seat. Said opening is closed by a flexible element (21) sealed on the edges of said opening.