Although the scientific community widely recognizes that backpack carriage in primary school children represents a critical issue, its consequences in terms of postural alterations and possible onset of musculoskeletal pathologies are still not fully understood. In particular, little information is available on the way load carriage modifies the foot-ground relationship in terms of plantar pressure distribution. This issue is of particular relevance, because the presence of a load alters the physiological weightbearing functions and, when mechanical overloading is repeated in time, it can act as a co-factor in promoting foot discomfort or pain. On the basis of these considerations, this study analyzed plantar pressure maps of 359 children attending primary schools (6-10 years old) under static upright posture conditions, to assess the magnitude and features of effects originated by load carriage on the foot-ground relationship. The collected data showed that backpack introduces significant increases in overall contact area (up to 10%) and in the plantar pressure peaks in midfoot and forefoot regions (20-30%). A significant shift in the average position of the center of pressure towards the forefoot was also observed, as an indicator of the body's attempt to restore the initial balance conditions threatened by the load. These results suggest that heavy loads, in the case of significant exposure times, may increase the risk of foot discomfort and act as a co-factor in the onset of foot structure alterations or pathologies.