Food sensory imagery - creating a vivid mental image of the sensory experience of eating - can lead to the selection of smaller portions because it serves as a reminder that eating enjoyment does not necessarily increase with portion size. The evidence is mostly limited to adults and to energy-dense foods for which it is particularly difficult to predict the satiating effects of consumption quantity. The objective was to study how food sensory imagery influences portion size selection of foods varying in energy density (brownie and applesauce) by 7- to 11-year-old children. During after-school time, 171 children were randomized into two conditions. Children in the food sensory imagery condition were asked to imagine the taste, smell, and texture of eating palatable foods, i.e., chocolate cereal, chocolate waffle, and chocolate candies. Children in the control condition performed a similar sensory imagery task for non-food-related activities. Children were then asked to choose between the recommended serving size, a 50% larger portion, and a 125% larger portion of either brownie or applesauce. One week later, they were placed in the same condition for the other food. Compared to the control condition, food sensory imagery led children to choose 7.1% less brownie but had no effect on applesauce portion selection. Exploratory findings showed that the food sensory imagery intervention was especially effective at reducing brownie portion size selection among children who were moderately hungry, who usually eat fast, and whose parents pressure them to eat. In conclusion, food sensory imagery may be a useful intervention to nudge children towards healthier portion size choices because it reduces the selected portion size of an energy-dense snack without reducing the selected portion size of a healthier snack.