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Associative Tool Use (ATU) describes the use of two or more tools in combination, with the literature further differentiating between Tool set use, Tool composite use, Sequential tool use and Secondary tool use. Research investigating the cognitive processes underlying ATU has shown that some primate and bird species spontaneously invent Tool set and Sequential tool use. Yet studies with humans are sparse. Whether children are also able to spontaneously invent ATU behaviours and at what age this ability emerges is poorly understood. We addressed this gap in the literature with two experiments involving preschoolers (E1, N = 66, 3 years 6 months to 4 years 9 months; E2, N = 119, 3 years 0 months to 6 years 10 months) who were administered novel tasks measuring Tool set, Metatool and Sequential tool use. Participants needed to solve the tasks individually, without the opportunity for social learning (except for enhancement effects). Children from 3 years of age spontaneously invented all of the types of investigated ATU behaviours. Success rates were low, suggesting that individual invention of ATU in novel tasks is still challenging for preschoolers. We discuss how future studies can use and expand our tasks to deepen our understanding of tool use and problem-solving in humans and non-human animals.

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The ratchet effect - the accumulation of beneficial changes in cultural products beyond a level that individuals could reach on their own - is a topic of increasing interest. It is currently debated which social learning mechanisms allow for the generation and transmission of cumulative culture. This study focused on transmission, investigating whether 4- to 6-year-old children were able to copy cumulative technological design and whether they could do so without action information (emulation). We adapted the spaghetti tower task, previously used to test for accumulation of culture in human adults. A baseline condition established that the demonstrated tower design was beyond the innovation skills of individual children this age and so represented a culture-dependent product for them. There were 2 demonstration conditions: a full demonstration (actions plus (end-)results) and an endstate- demonstration (end-results only). Children in both demonstration conditions built taller towers than those in the baseline. Crucially, in both demonstration conditions some children also copied the demonstrated tower. We provide the first evidence that young children learn from, and that some of them even copy, cumulative technological design, and that - in line with some adult studies - action information is not always necessary to transmit culture-dependent traits.

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The variety and complexity of human-made tools are unique in the animal kingdom. Research investigating why human tool use is special has focused on the role of social learning: while non-human great apes acquire tool-use behaviours mostly by individual (re-)inventions, modern humans use imitation and teaching to accumulate innovations over time. However, little is known about tool-use behaviours that humans can invent individually, i.e. without cultural knowledge. We presented 2- to 3.5-year-old children with 12 problem-solving tasks based on tool-use behaviours shown by great apes. Spontaneous tool use was observed in 11 tasks. Additionally, tasks which occurred more frequently in wild great apes were also solved more frequently by human children. Our results demonstrate great similarity in the spontaneous tool-use abilities of human children and great apes, indicating that the physical cognition underlying tool use shows large overlaps across the great ape species. This suggests that humans are neither born with special physical cognition skills, nor that these skills have degraded due to our species' long reliance of social learning in the tool-use domain.

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Five- and 6-year-olds (N=51) heard stories in which a character sorted items into two locations. Either the character had a false belief about one of the items (e.g., thought a tin contained biscuits, not Lego), or was only partially informed of an item's dual identity (e.g., did not know that a tie was a present). Children found it easier to reject a report of the character's belief that described the true state of affairs when the character had a false belief (e.g., Is Fred's uncle thinking "where shall I put this Lego?"), than to reject one in which an object known to the character was described using a term of which she was ignorant (e.g., Is Mum thinking "where shall I put this present?"). Similarly, children found it easier to predict the character's incorrect sorting of the target items for false belief (with food not toys) than for dual identity (in the wardrobe not with things to take on a visit). Correct reasoning about beliefs and reports of beliefs that misrepresent an object does not imply mastery of the fact that beliefs represent an object in a particular way.

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Children's concurrent success on false belief tasks and their handling of two labels for one object (e.g., bunny/rabbit) has been interpreted as demonstrating understanding about the essential features of representation. Three experiments reveal the limitations in 5-year-olds' understanding for both mental and linguistic representations. We report relatively poor performance on a task involving two labels for one object (e.g., dice/eraser) which required children to treat another's knowledge as representing only some of the feature of its real referent: Dice but not eraser. Five year olds who made errors also had difficulty handling the fact that a written word 'dice' referring to such a dice/eraser, can also be applied to a standard dice but not to a standard eraser. These children lacked metalinguistic awareness of words as entities that both refer and describe.

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Thirty-nine 6-year-old children participated in a longitudinal study using tasks that required handling of dual identity. Pre- and posttest sessions employed tasks involving a protagonist who was partially informed about an object or person; for example, he knew an item as a ball but not as a present. Children who judged correctly that the protagonist did not know the ball was a present (thereby demonstrating some understanding of the consequences of limited information access), often judged incorrectly (1) that he knew that there was a present in the box, and (2) that he would search as if fully informed. Intervening sessions added contextual support and tried to clarify the experimenter's communicative intentions in a range of ways. Despite signs of general improvement, the distinctive pattern of errors persisted in every case. These findings go beyond previous studies of children's handling of limited information access, and are hard to accommodate within existing accounts of developing understanding of the mind.

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We identify a surprising discrepancy in children's performance in two tasks which appear superficially to require handling of the same properties of the representational mind. Four- to six-year-olds made judgements about the knowledge of a protagonist who had only partial information about an object: the child knew that an object in a box had two descriptions, X and Y (e.g. dice and eraser), but the protagonist had access to only one of these, X. In Experiment 1, children who passed a standard false-belief task also judged correctly that the protagonist did not know the X was Y, but often judged wrongly that he did know there was a Y in the box. In Experiment 2, children predicted wrongly where the protagonist would look for a Y: the problem was not purely linguistic. We argue that success on standard theory-of-mind tasks can be supported by a more basic representing ability than is assumed in current theories, and that children's mental representation of referential relations between the world and the mind subsequently undergoes important change.

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