In the early period of language acquisition many children use fillers, namely, they start adding monosyllabic elements in front of words they used earlier, and may continue to use, without such elements. For example, the sound /∂/, in ∂dog for English, and in /∂pε̃/ 'pain' [bread] for French. In some accounts, fillers are considered early manifestations of grammatical morphemes; in others, phonoprosodic phenomena from which, later, grammatical morphemes develop. The aim of this presentation is to trace the development of fillers in the longitudinal data of four children acquiring French, studied between the ages of 1;3/1;9 and 2;0/2;3. Children were recorded audio-visually, at least once a month, while they interacted naturally in their home environment. The data were transcribed in CHAT format, phonologically for the children and in French orthography for the adults, and were linked to the videos. All the lexical items whose targets were nouns and verbs in French were coded for the presence and type of elements occurring at the onset of the lexeme, and specific phonoprosodic and morphosyntactic hypotheses were tested. Results suggest that fillers cannot be lumped together in a single bag. Indeed, they indicate the existence of three main periods in fillers' production: 1. pre-morphological, where fillers mainly fulfill phonoprosodic functions; 2. proto-morphological, where fillers present incipient properties of grammatical morphemes, hinted by an overall differentiation between noun and verb fillers; and 3. quasi-morphological, where fillers co-occur with well-formed grammatical morphemes, sometimes for the same lexeme, and with developments in children's verbal production. In all three periods, fillers and grammatical morphemes do not reach criterion in obligatory contexts. The discussion highlights the importance of the developments in fillers' production for understanding the nature of early morphological acquisition.