Improving children's abilities to recognize when they are full is one strategy to prevent overweight, but currently, there are few validated instruments to assist this process. In the present study, we developed and tested the potential of an analog scaling device for quantifying sensations such as fullness in 4-5 year old children. The device was a picture of a doll with a rectangular stomach over which a sliding bar could be moved to communicate rated fullness levels. Eleven 4-5 year old children were shown pictures of French fries and fruit salad in five varying portion sizes that increased in diameter exponentially by a power of 1.5, ranging from 5.2 to 18.5 cm. Success in using the device was predefined as an increase in ratings as a function of increasing portion size, in at least one of two trials. Eight children were successful with the fries, and ten were successful with the fruit salad. Mean ratings across children were significantly different from each other for both foods. These data show that children can be trained to use an analog scale to quantify differences in portion sizes of foods. Future experiments will validate this scaling procedure for measuring fullness in real eating situations. If successful, this methodology might have applications to the measurement of other bodily sensations in young children.