A foldable stroller frame has three sections (lower-front, lower-rear, and upper-rear sections) joined to and foldable around a common hub structure. The hub structure includes two hubs located on the left and right sides of the stroller frame. In at least one of the hubs, a bracket structure is mounted to the lower-rear section and holds two gears which are attached to the lower-front section and upper-rear section, respectively. The two gears are engaged with each other, so that the lower-front section and upper-rear section rotate in synchrony with respect to the lower-rear section when the stroller frame is being folded. The hub also includes a releasable locking mechanism, which is controlled by a pull trigger located on the upper-rear section of the stroller near the push handles, for locking the stroller frame in the unfolded state.