This study investigated relations between social interaction during infancy and children's subsequent theory of mind (ToM). Infant-mother pairs (N = 57) were observed in a free-play context at 6 months. Interactions were coded for (a) mothers' use of mental state language that commented appropriately on the infants' mental states, and (b) mothers' use of mental state language that did not appropriately reflect their infants' minds. A third variable was (c) security of attachment, which was assessed using the Strange Situation procedure at 12 months. Performance on a battery of ToM tasks at 45 and 48 months was positively correlated with (a), but was not related to (b) or (c). A regression analysis showed that mothers' use of appropriate mental state comments independently predicted overall ToM performance, accounting for 11% of the variance. Children's verbal ability was the only other independent predictor of ToM performance, accounting for 16% of the variance. These findings represent the earliest known social predictor of individual differences in ToM.

The construct validity of maternal mind-mindedness (MM) was investigated in the context of its relations with children's later understanding of mind. MM measures were obtained from infant-mother (N = 52) interactions at 6 months, and from maternal interviews at 48 months. Children's understanding of mind was assessed using theory of mind (ToM) tasks at 45 and 48 months, and a stream of consciousness (SoC) task at 55 months. One of the early MM measures--mothers' appropriate mind-related comments--was a positive independent predictor of: (a) MM at 48 months, and (b) ToM and SoC performance at 45 to 55 months. Path analyses suggested direct links between mothers' use of appropriate mind-related comments and children's later understanding of mind.