Background: Parents have important roles to perceive the growth abnormalities of their children. Parental misperception can affect the children's long-term health problems. Aim: To investigate: (a) the accuracy of parents' perception of children's weight, height, and body shape, (b) the effects of misperception in caring for children's health, and (c) the factors of parental misperception. Methods: A cross-sectional study was conducted at a primary school in Bangkok, Thailand. A total of 1,153 parents completed self-administered questionnaires: (1) verbal perception of children's weight and height and (2) visual perception of children's body shape using Children's Body Image Scale developed by Truby H and Paxtron SJ. Results: The agreement of parents' perception and children's actual weight and height was fair (K = 0.33 and 0.27, respectively). While the agreement of parents' perception of boys' and girls' body shape was moderate (K = 0.43 and 0.48, respectively). Parents who underestimated children's weight and height were likely to seek medical care (OR = 1.92; 95% CI 1.39, 2.65 and OR = 3.73; 95% CI 2.56, 5.44, respectively). Nonetheless, parents tended to underestimate the boys' weight. Conclusion: Many parents do not accurately perceive their children's weight, height, and body shape. This misperception could influence their caring for children's health. Thus, educating parents about the perception of children's growth should be emphasized to avoid long-term health effects.