The learning and generalisation of grammatical regularities is fundamental to successful language acquisition and use. Research into statistical learning has started to consider how this process occurs through the implicit detection and assimilation of grammatical regularities. This study focuses on how adults and children generalise regularities and explores the role of explicit knowledge in this process. Across three experiments, adults and children learnt an artificial language containing two semantic categories denoted by a co-occurring determiner and suffix. Explicit knowledge of the regularities was associated with generalisation performance in adults but not children, even when adult word level knowledge was similar to children’s. The implications of these results for developmental theories of grammatical generalisation are discussed.