Symbols are used regularly in our daily lives, but in order for a symbol to serve its intended purpose, its meaning must be conveyed in some way (Myers & Liben, 2012). Across two studies, this research examined 4- to 6-year-olds' understanding of how the relations between symbols and their referents are effectively conveyed using legends. To investigate this issue, a novel task was developed in which it was necessary to convey the arbitrary correspondence between symbols (the shapes on top of a set of boxes) and a set of referents (cards with shapes on them), so that an unknowing other would know which card went inside each box. Study One was an investigation of children’s ability to evaluate legends that either effectively or ineffectively conveyed symbol-referent relations. Children’s performance was examined in relation to age, the ability to detect ambiguity (Ambiguous Messages and Droodle tasks), and Executive Function skills (Inhibitory Control, Working Memory, Planning tasks). The results provide evidence that both the ability to detect ambiguity and Executive Function uniquely relate to children’s ability to evaluate legends. Study Two investigated a new group of children’s ability to create a legend to convey symbol-referent pairs, in relation to the same cognitive skills considered in Study One. In addition, to examine the impact of exposure to effective legends, half of the children who did not create an effective legend were then presented with legends created by the experimenter, while the other half served as the baseline group. Children who received this exposure, relative to those in the baseline group, significantly improved their legend creations and transferred this improvement to a new set of stimuli. This study found evidence that ambiguity detection was related both to legend creation on children’s first attempt, and children’s ability to improve following exposure. However, Executive Function performance did not relate to legend production. Taken together, these studies provide insight on factors that relate to children’s developing understanding of how symbol meanings are effectively conveyed, and argue for the important role of being able to detect ambiguity.