Ontogeny of tool use: how do toddlers use hammers?

Hammering with a hand tool appears early in life. Skillful hammering involves accommodating movements to properties of the hammer, orienting the hammer's head to the item to be struck, and maintaining stable posture during forceful action with the arm(s). We aimed to characterize development of these abilities in young children (12, 18, and 24 months old). Children struck at a peg with a hammer held in the hand or a hammer attached to a handle. Children struck more frequently with a hard hammer surface than a soft one, and more frequently (although less accurately) with handled hammers than with non-handled hammers. Developmental differences were evident in accuracy, number of strikes, and kinematic parameters, especially with the handled object. Children's ability to use objects for forceful and accurate percussion changed measurably over the second year, in tandem with improving postural stability and greater motion of the elbow.