Infancy/Toddlerhood. 6 months infant look at, vocalize to, smile at, and touch other infants, thereby distinguishing themselves from others (Hay et al., 2009). As babies develop, relations with peers change, becoming more reciprocal. e.g. at about a year, their smiles, vocalizations, and playful activities are often imitated or reacted to (Howes & Matheson, 1992). During the second year, toddlers use words to communicate and can coordinate their behavior with that of a playmate (Rubin et al., 2006).