Two studies assessed a breadth of older siblings effect - whether it includes better understanding of other than beliefs mental states, and what is the role of pretend play and inhibitory control in the mechanism of the effect. In study 1 with ninety-one children between 3 and 4 years there were used false belief tasks with additional questions investigating understanding of conflicting desires and surprise, and behavioural measures of pretend play. It was found that having older siblings was an independent from pretence source of variance in false beliefs understanding and was not associated with better understanding of other than beliefs mental states. In study 2 with 72 children between 3 and 5 years there were used false and true belief tasks and DCCS as a measure of inhibitory control (IC). Number of older siblings was not an independent from IC source of variance in false beliefs understanding. Both studies indicate that having older siblings is linked with a local but not global facilitation effect in ToM development, and that a pretend play is not a main mechanism involved in this effect.
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