The present invention relates to a special structure for child safety seats intended to be used in motor vehicles that significantly reinforces them in order to resist, with greater guarantees, the crash or collision to which vehicles are exposed, both in the event of colliding with another vehicle and in the event of colliding with a certain obstacle.This new and advantageous structure for child safety seats comprises a seat rest, a backrest, two sides and a headrest, formed by a rigid frame. More specifically, it basically comprises a base frame, a backwards frame tilted joined at the bottom to the front part of the base frame and a vertical support solidly connected to the base frame and to the tilted frame, whose frame receives the coupling of components that constitute the support of the constituent parts of the seat, such as the base, sides and headrest, whose parts are formed from blocks of pressure-absorbing lightweight material.