Abstract: Closure system for a children's drinking bottle or a children's drinking cup comprising a sealing ring which has on an external periphery a fastening means for sealingly and releasably connecting to a container edge of a container of the children's drinking bottle or the children's drinking cup, an aperture for receiving a mouthpiece and/or a blind lid and an internal thread, which borders the aperture and is arranged at a distance from the aperture and the fastening means and a fixing insert with a through aperture and an external thread which may be screwed into the internal thread of the sealing ring in order to clamp sealingly a fastening attachment of the mouthpiece and/or the blind lid between the fixing insert and the sealing ring.