Children with low birth weight (LBW) often exhibit poorer social and cognitive abilities than their normal birth weight (NBW) peers. These difficulties may persist into young adulthood and are accompanied by altered resting-state electroneurophysiological patterns. Considering the results of these studies, understanding the neural substrates of birth weight becomes more important. Here, we used EEG event-related oscillations to unravel differences between children born with low and normal birth weights during a visual memory encoding to explore further the birth weight effect on the brain oscillatory responses of 6-to-7-year-old children. This study used an observational, cross-sectional, between-group design comparing LBW/preterm (N = 15) and NBW (N = 17) children. EEGs of the children were recorded during the encoding phase of visual memory task. Additionally, all children were administered two subtests from the WISC-IV IQ assessment: working memory (WM) and processing speed (PS). We employed time-frequency analysis to investigate event-related brain oscillatory pattern to distinguish differentiation between LBW/preterm and NBW. Consistent with previous studies, our behavioral results demonstrated that LBW/preterm group scored worse on WM and PS than their NBW peers. EEG results highlighted a topological differentiation between LBW/preterm and NBW groups, with greater posterior event-related alpha and especially beta responses in the LBW/preterm group during item encoding. Importantly, posterior beta oscillatory responses negatively correlated with the PS score in NBW children. Based on our results, the differences in cognitive abilities in the LBW/preterm group may be associated with posterior overactivity, characterized by increased event-related alpha and beta responses. This overactivity may reflect a greater reliance on perceptual processing strategies during memory encoding in early school-aged children born with low birth weight. This has potential implications for tailoring educational strategies to their unique neurodevelopmental profiles.