Category clustering is a strategy that is often used in free-recall tasks with semantically related items. Age differences in recall performance have been shown to be attributable to age differences in learning to cluster (Horn et al., 2021; Michalkiewicz et al., 2020). Theories of memory development predict age differences in the use of support for category clustering (Flavell, 1970). We hypothesized that simultaneous item presentation would support clustering in children. We presented 45 seven-year-old children, 30 ten-year-old children and 60 young adults with 36 stimulus pictures that were clusterable in pairs on semantic grounds, followed by free recall. The two stimulus pictures from the same category were presented either simultaneously or sequentially on a computer screen. Using multinomial processing tree modelling (Batchelder & Riefer, 1986), we disentangled cluster encoding, cluster retrieval, and singleton recall. Results showed that presentation mode affected cluster encoding. Simultaneous presentation, compared to sequential presentation, led to higher probability of cluster encoding in all age groups. Cluster retrieval or singleton recall was not affected by presentation mode. Simultaneous presentation may facilitate encoding as clusters by enhancing common feature identification of category information (Carvalho & Goldstone, 2014). Implications regarding theories of memory development are discussed.