The world within: Children are sensitive to internal complexity cues

When reasoning about the mechanisms of complex entities, it is important to consider their internal parts. Previous research has shown that young children view "insides" as critical to how objects function. However, whether children hold specific expectations regarding complex objects' insides remains an open question. Here, children (n = 378) and adults (n = 124) made internal and causal complexity judgments regarding real-world objects. In Study 1, 5- and 6-year-olds, but not 4-year-olds, succeeded at internal complexity judgments and matched complex artifacts with complex insides. All age groups succeeded at causal complexity judgments and identified complex artifacts as causally complex. Study 2 tested whether the internal complexity cues of number/area, diversity, and connections of internal parts conveyed complexity to children. The 5-year-olds were sensitive only to number/area of internal parts as a complexity cue, but the older children and adults were sensitive to all three cues plus number of parts when controlling for area (Study 3). Despite limited exposure to insides, even young school-age children hold detailed and abstract expectations concerning internal complexity.