Working memory (WM) is a critical cognitive system that supports processing a variety of information. Remembering different types of objects may impose different levels of cognitive demands on WM performance. In the present study, we examined 205 children's WM in representing different types of content and its developmental trajectories in early childhood. Experiment 1 examined 5-year-olds' WM performance when remembering different content (animals and dots). To control perceptual differences, Experiment 2 compared the same-age children's WM performance when the stimuli (e.g., three dots) needed to be encoded from different representational domains (perceptual domain: visuospatial representation; conceptual domain: numerical representation). In Experiment 3, we further investigated the early developmental trends of representing different types of information in WM between the ages of 3 and 5. Results showed that children's WM performance varied over different types of stimuli. When presented with the same stimuli, encoding different aspects of the content (conceptual vs. perceptual) may impose different levels of cognitive demands, and the performance of which was dependent on the WM loads. Together these findings informed our understanding of the role of representational content in children's WM development and provided empirical implications for considering the testing stimuli when designing WM measurements for young children.