Within the Time-Based Resource-Sharing (TBRS) model, we tested a new conception of the relationships between processing and storage in which the core mechanisms of WM are time constrained. However, our previous studies were restricted to adults. The present study aimed at demonstrating that these mechanisms are present and functional before adulthood. For this purpose, we investigated the effect on maintenance of the duration of the attentional capture induced by processing. In two experiments using computer-paced WM span tasks, 10- year-old children were asked to maintain letters while performing spatial location judgments. The duration of this processing was manipulated by varying either the discriminability between target locations or the contrast between targets and background. In both experiments, as we previously observed in adults, longer processing times resulted in poorer recall. These findings suggest that the core mechanisms of WM described by the TBRS model are already settled in childhood.