Abstract: This structure comprises an upright (1), a sliding block (3) sliding on the upright (1) along an axis (XX?), and at least a collapsible leg (5) associated with a jointed structure (7). This structure comprises, seen according to a direction (Y-Y?) different from said axis (X-X?), a jointed deployment triangle (21) having a first side (22) delimited by a first joint (23) located on the upright (1) and a second joint (25) located on a point of the sliding block (3). The first joint (25) or the second joint (23) comprises two points of joint (35) separated according to said direction (Y-Y?) so that the side of the deployment triangle (21) which is jointed at these two points (35) constitutes a rigid guiding triangle (29) defined by these two points (35) and by a third joint (31). Application to the collapsible structures of children pushchairs.