The phonological rhythm of French is characterized by a tendency to syllabic isochrony within an utterance and a clear final lengthening, whereas the rhythm of English is stress-timed. A study of babbling at a turning period of the child's development has shown that the French child acquires adult phonological rhythm quite early in interactive situations. There is a strict initial isochrony followed progressively towards 13 months by a final lengthening that, from 16 months on, is the same as in adult speech. This kind of rhythm is not found in solitary play. A review of literature on English babbling indicates that things are not so clear in the acquisition of phonological rhythm in this language, as its main characteristic, which is stress, seems to be acquired quite late. (Contains 79 references.) (Author)