The invention relates to a closing system for a child's drinking bottle or a child's drinking cup having a closing ring (20), which comprises a mounting means (40) on an outer circumference for sealingly and releaseably connecting to a container edge (16) of a container (10) of the child's drinking bottle or child's drinking cup, an opening (36) for receiving a mouthpiece (22) and/or a blind cover (32), and an internal thread (46), which surrounds the opening and is disposed at a distance from the opening and from the mounting means, and a fixing insert (30) having a passage opening (6) and an external thread (66) that can be screwed into the internal thread of the closing ring in order to sealingly clamp a mounting lip of the mouthpiece or blind cover between the fixing insert and the closing ring.