Convertible carriage that is book-like foldable and that is usable as a push frame for baby strollers comprising: - a pair of front legs, respectively a front right leg and a front left leg that are parallel to one another, laterally spaced and associated with one another in order to constitute a unique body and that are provided with at least one front wheel for resting on the ground, - a pair of rear legs, respectively a rear right leg and a rear left leg which are parallel to one another, laterally spaced and associated with each other in order to constitute a unique body and that are provided with at least one rear wheel for resting on the ground, and - a pair of operating shafts, respectively a right operating shaft and a left operating shaft that are parallel to one another, laterally spaced and associated with one another in order to constitute a unique body and that are provided with at least one handle, - wherein said pair of rear legs and said pair of front legs are articulated in a rotatable manner around a common first hinge axis or around an own first distinct hinge axis defined in an articulation joint, wherein said first hinge axis is parallel to the supporting ground of said carriage and orthogonal to the displacement direction of said carriage, characterized in that it comprises - a pair of plate-like bodies (22, 23) that are interposed between said pair of front legs and said pair of rear legs, are articulated to one another, at one end, around a second hinge axis and are articulated, at the opposite end, to said pair of front legs and to said pair of rear legs respectively around a third hinge axis and a fourth hinge axis, wherein said hinge axes are parallel to one another and distinct and wherein said carriage takes up an open configuration, in which said pair of front legs and said pair of rear legs are spaced apart from one another, said plate-like bodies (22, 23) extend between them and are substantially coplanar to one another and said operating shafts extend upwardly and rearwardly of said pair of front legs, and a closed configuration, in which said pair of front legs, said pair of rear legs and said pair of operating shafts are close to one another and at least partially overlapped and said plate-like bodies (22, 23) are juxtaposed to one another and at least partially overlapped and interposed between said pair of front legs and said pair of rear legs, wherein when said carriage is in said open configuration, said pair of plate-like bodies (22, 23) acts as a supporting plane that supports the bottom of a bellows-like foldable basket that is interposed between said pair of front legs and said pair of rear legs and the upper edge of which is associated with said pair of front legs and with said pair of rear legs. - a pair of front legs, respectively a front right leg and a front left leg that are parallel to one another, laterally spaced and associated with one another in order to constitute a unique body and that are provided with at least one front wheel for resting on the ground, - a pair of rear legs, respectively a rear right leg and a rear left leg which are parallel to one another, laterally spaced and associated with each other in order to constitute a unique body and that are provided with at least one rear wheel for resting on the ground, and - a pair of operating shafts, respectively a right operating shaft and a left operating shaft that are parallel to one another, laterally spaced and associated with one another in order to constitute a unique body and that are provided with at least one handle, - wherein said pair of rear legs and said pair of front legs are articulated in a rotatable manner around a common first hinge axis or around an own first distinct hinge axis defined in an articulation joint, wherein said first hinge axis is parallel to the supporting ground of said carriage and orthogonal to the displacement direction of said carriage, - a pair of plate-like bodies (22, 23) that are interposed between said pair of front legs and said pair of rear legs, are articulated to one another, at one end, around a second hinge axis and are articulated, at the opposite end, to said pair of front legs and to said pair of rear legs respectively around a third hinge axis and a fourth hinge axis, wherein said hinge axes are parallel to one another and distinct and wherein said carriage takes up an open configuration, in which said pair of front legs and said pair of rear legs are spaced apart from one another, said plate-like bodies (22, 23) extend between them and are substantially coplanar to one another and said operating shafts extend upwardly and rearwardly of said pair of front legs, and a closed configuration, in which said pair of front legs, said pair of rear legs and said pair of operating shafts are close to one another and at least partially overlapped and said plate-like bodies (22, 23) are juxtaposed to one another and at least partially overlapped and interposed between said pair of front legs and said pair of rear legs, wherein when said carriage is in said open configuration, said pair of plate-like bodies (22, 23) acts as a supporting plane that supports the bottom of a bellows-like foldable basket that is interposed between said pair of front legs and said pair of rear legs and the upper edge of which is associated with said pair of front legs and with said pair of rear legs.