This narrative review aimed to elucidate which robot-related characteristics predict relationship formation between typically-developing children and social robots in terms of closeness and trust. Moreover, we wanted to know to what extent relationship formation can be explained by children's experiential and cognitive states during interaction with a robot. We reviewed 86 journal articles and conference proceedings published between 2000 and 2017. In terms of predictors, robots' responsiveness and role, as well as strategic and emotional interaction between robot and child, increased closeness between the child and the robot. Findings about whether robot features predict children's trust in robots were inconsistent. In terms of children's experiential and cognitive states during interaction with a robot, robot characteristics and interaction styles were associated with two experiential states: engagement and enjoyment/liking. The literature hardly addressed the impact of experiential and cognitive states on closeness and trust. Comparisons of children's interactions with robots, adults, and objects showed that robots are perceived as neither animate nor inanimate, and that they are entities with whom children will likely form social relationships. Younger children experienced more enjoyment, were less sensitive to a robot's interaction style, and were more prone to anthropomorphic tendencies and effects than older children. Tailoring a robot's sex to that of a child mainly appealed to boys.

Previous research has suggested that robotmediated therapy is effective in the treatment of children with Autism Spectrum Disorder (ASD), but not all robots seem equally appropriate for this purpose. We investigated in an exploratory study whether a robot's intonation (monotonous vs. normal) and bodily appearance (mechanical vs. humanized) influence the treatment outcomes of Pivotal Response Treatment (PRT) sessions for children with ASD. The children (age range 4-8 years) played puzzle games with a robot which required communication with the robot. The treatment outcomes were measured in terms of both task performance and affective states. We have found that intonation and bodily appearance have an effect on children's affective states but not on task performance. Specifically, humanized bodily appearance leads to more positive affective states in general and a higher degree of interest in the interaction than mechanical bodily appearance. Congruence between bodily appearance and intonation triggers a higher degree of happiness in children with ASD than incongruence between these two factors.

Social robots and their interactions with children are becoming increasingly sophisticated, with the emergence of child-robot relationships as a likely result. However, adequate measurement instruments that tap into concepts associated with child-robot relationship formation are scarce. We aimed to develop three measures that can be used to assess children’s closeness to, trust in, and perceived social support from, a social robot. We established the validity and reliability of these measures among 87 Dutch children aged 7 to 11 years old. Because of their shortness, the measures can efficiently be applied by scholars aiming to gain insight into the general process of child-robot relationship formation and its specific sub-processes, that is, the emergence of closeness, trust, and perceived social support.

Social robots and the Internet of Toys present key technologies in children's future life.Based on Winfield (2012), we conceptualize the relationship between social robots and smart/connected toys with six characteristics: interactivity, energy, sensors, software-control, movement, and embodiment. These characteristics, in turn, help to classify social robots and smart/connected toys along three dimensions (i.e., horizontal, vertical, and spatial integration), which suggests that social robots and smart/connected toys differ gradually rather than categorically. We identify three common theoretical (absence or heterogeneity of theory, lacking developmental perspective, insufficient attention to intercultural differences) and three methodological issues (lack of standardized measures, study design issues, dominance of cross-sectional studies) that research on both social robots and the Internet of Toys needs to address.

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