This work analysed the evolution of generalized motility from normal birth (39 to 40 weeks of gestational age) to six months of age, in 73 healthy infants during sleep, according to age. Sleep polygraphic recordings were performed in the morning; body movements were recorded with piezo-electric accelerometers. Our results showed that the number of movements per sleep hour was higher in active sleep (AS) as compared to quiet sleep (QS) whatever the age although the difference was less important in neonates (P < 0.05) than after one month of life (P < 0.001). The number of movements and the percentage of time spent in movements decreased with age; however in QS these parameters decreased sharply from birth to one month and a half but then did not significantly differ; in AS they became progressively lower. There were no statistically significant differences in the duration of body movements between sleep states in each age group; their mean duration became shorter from birth to six months of age (in AS P < 0.0001 and in QS P < 0.05). The distributions of the number of movements throughout the sleep stage were different according to sleep state and age. The movements were equally distributed during AS whatever the age and in the neonate group during QS; in older infants, the number of movements increased at the beginning and at the end of QS stages. During the first six months of life, spontaneous motility during sleep was inhibited, however, this process differed in quiet and active sleep. The relationship between body movements and sleep stages' organisation became closer during maturation.