Recent findings indicate substantial changes between the ages of 18- and 24-months in children’s integration of object properties with their actions on objects. Here we report new results from shape sorting and posting tasks in an attempt to understanding how motor and visual developments (or their combination) may contribute to this period of rapid development. Toddlers aged 18-months participated in four experiments involving inserting objects into openings. Results suggest that the key developmental achievements reside not in visual or motor developments alone, but in their integration.