There is considerable evidence that adults' perception of body weight in others can be manipulated via visual exposure to multiple bodies at one or another weight extreme. No study has yet examined how early in childhood such visual adaptation aftereffects exist. We ran experimental adaptation tests with predominantly White British 11- and 12-year-olds, 14- and 15-year-olds, and adult men and women (Study 1
N = 181) and with 7- and 11-year-olds and adults (Study 2
N = 110). Participants viewed bodies ranging from low to high weight before and after being adapted to bodies with very low or very high body mass. Participants of all ages showed a significant change in their weight estimates after being adapted to larger bodies (but not to smaller bodies), suggesting that this aspect of body perception is functionally mature by 7 years.