Provided is a playpen for children. A lower frame comprises a center seat located in the middle, and a plurality of bottom connecting rod sets connected between the center seat and corresponding lowerframe angle joints, the center seat comprises an upper center set and a lower center set which can do displacement up and down correspondingly, a triangular mechanism capable of deforming is formed by each bottom connecting rod set, the upper center set and the lower center set, and four-connecting-rod mechanisms capable of deforming are formed by the bottom connecting rod sets and stand rods. When the playpen for the children is located at an unfolded position, the lower frame is stable in structure. When the upper center set relatively move upwards relative to the lower center set, the triangular mechanisms and the four-connecting-rod mechanisms deform at the same time, the stand rods can be promoted to keep upright or close to the center synchronously nearly uprightly, and the whole playpen is promoted to be folded and closed.