People infer that individuals are socially related if they have overlapping preferences, beliefs, and choices. Here we examined whether people also infer relationships by attending to social network information. In five preregistered experiments, participants were shown the social networks of two target people and their friends or acquaintances within a group, and judged if the targets were socially related to one another. In the first three experiments, adults (total N = 528) were more likely to judge that individuals were friends when a high rather than low proportion of their friendships were mutual. Adults also considered other factors when inferring friendships, such as the number of friends each individual had. In the final two experiments, 5–7-year-olds (total N = 135) were also sensitive to the proportion of mutual relationships. Together, our work suggests that people use proportional information and statistical inferences when assessing whether individuals are socially related.

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People are sometimes drawn to novel items, but other times prefer familiar ones. In the present research we show, though, that both children’s and adults’ preferences for novel versus familiar items depend on their goals. Across four experiments, we showed 4- to 7-year-olds (total N = 498) and adults (total N = 659) pairs of artifacts where one was familiar and the other was novel (e.g., a four-legged chair and ten-legged chair). In Experiment 1 , children wanted to have familiar artifacts, but to learn about novel ones. Experiment 2 replicated this pattern using a simpler procedure, and found the same pattern in adults. In Experiment 3 , 4- to 6-year-olds and adults more strongly preferred familiar items when choosing which they would rather have than when choosing which they would rather try using. Finally, Experiment 4 replicated adults’ preferences to have familiar items and learn about novel ones with an additional set of items. Together these findings show that preferences for novelty depend on people’s goals. We suggest these effects arise because children and adults are motivated both by the promise of information and the desire for safe options in high commitment decisions that entail risk. Supplementary Information The online version contains supplementary material available at 10.3758/s13423-022-02118-9.

Young children anticipate that others act rationally in light of their beliefs and desires, and environmental constraints. However, little is known about whether children anticipate others’ irrational choices. We investigated young children's ability to predict that sunk costs can lead to irrational choices. Across four experiments, 5‐ to 6‐year‐olds (total N = 185) and adults (total N = 117) judged which of two identical objects an agent would keep, one obtained at a high cost or one obtained at a low cost. In Experiment 1, adults predicted that the agent would choose the high‐cost object over the low‐cost one, whereas children responded at chance. Experiment 2 replicated these findings in children, but also included another condition which showed they were sensitive to future costs. They predicted that an agent would be more likely to seek out a low‐cost item than a high‐cost item. Experiments 3 and 4 then found that children do not anticipate the sunk cost bias in first person scenarios, or in interpersonal sunk cost scenarios, where costs are sunk by others. Taken together, our findings suggest that young children may struggle to understand and predict irrational behavior. The findings also reveal an asymmetry between how they consider sunk costs and future costs in understanding actions. We propose that this asymmetry might arise because children do not consider sunk costs as wasted.