By 3?years of age, children generally have a firm understanding of others' reliability, but there is considerable variation among individual children. Little attention has been paid to factors that influence such individual differences. This study addressed this by assessing the relation between reliability understanding and temperament in children approaching their third birthday. We measured children's ability to judge a speaker's trustworthiness and to selectively learn new information from a reliable informant. Observer ratings provided assessments of children's activity, task orientation, and affect/extraversion. Significant associations between selective trust and the temperament dimension of affect/extraversion were found, along with associations between selective trust and gender and language ability. This indicates that the ability to ascertain whether a speaker is a reliable person from whom to learn is related to several individual child characteristics.