Maternal perceptions, about the nutritional status of their children, may have implications for timely health care seeking and feeding behaviour. Shreds of evidence are limited in this area that assessed maternal perception about the nutritional status of the children in the context of Bangladesh. The objective of this study is to assess the differences in mothers' perceptions about their children's nutritional status who are less than 5 years of age and their associated factors in the context of urban slum areas. A cross-sectional study (Quantitative approach) was conducted in two of the largest urban slums of Dhaka city. A total of 437 mother-children dyads were included in the final analysis. The outcome of interest was the mother's 'varied perceptions' regarding the nutritional status of their children under five. 'Varied perception' refers to the difference between a mother's subjective assessment of her child's nutritional condition and the anthropometrically measured nutritional status. The prevalence of mother's varied perceptions was around 46%, and among them, 37% of mothers underestimated and 9% overestimated their child's nutritional status. 'The child doesn't want to eat' (AOR = 3.69; 95% CI: 2.34-5.85; p < 0.001) and 'Feels light when carried' (AOR = 3.39; 95% CI: 1.69-6.81; p = 0.001) were the significant reasons behind the mother's perception about the nutritional status of their under-five children. About one in two mothers' perceptions about their children varied from the anthropometry-derived status. Various research findings indicate that providing health education on proper feeding practices for children, along with anthropometric measurements, can assist mothers in enhancing their understanding and assessing their child's nutritional status with greater accuracy. Further qualitative research may be instrumental in getting deeper insights into maternal perception to develop context-specific interventions.