Most previous research on non-nutritive sucking habits has been cross-sectional in nature. This study determined the prevalence of non-nutritive sucking habits and the effects on the developing dentition within a longitudinal observational cohort. The Children in Focus group of the Avon Longitudinal Study of Pregnancy and Childhood study was studied. Questionnaire data on non-nutritive sucking habits were collected on the children at 15 months, 24 months, and 36 months of age. Dental examinations were performed on the same children at 31 months, 43 months, and 61 months of age. At 15 months, 63.2% of children had a sucking habit, 37.6% used just a dummy, and 22.8% used a digit. By 36 months, sucking had reduced to 40%, with similar prevalence of dummy and digit sucking. Both habits had effects on the developing dentition, most notably in upper labial segment alignment and the development of anterior open bites and posterior crossbites. The majority of children had non-nutritive sucking habits up until 24 months of age. Both digit and dummy sucking were associated with observed anomalies in the developing dentition, but dummy-sucking habits had the most profound influence on the anterior and posterior occlusions of the children.