The utility model relates to a two-purpose assembling and disassembling structure for children's bikes, which comprises a wheel shaft, a crank and a pedal, wherein column holes with non-circular sections are arranged at the middle parts of both ends of the wheel shaft, and indentations are arranged on the inner walls of the column holes; one end of the crank is pivoted with the pedal, a scarf joint segment is arranged on the other end, and a fastening tenon is arranged at the scarf joint segment to be correspondingly jogged with the column holes of the wheel shaft and the indentations on the inner walls of the column holes; the crank and the pedal on the crank can be replaced, wherein the column holes can be transversally communicated with perforation holes, and an elastic button is arranged on the crank for correspondingly buckling, which benefits for pressing the elastic button to disassemble. The utility model is suitable for the rapid disassembly and replacement of the crank pedal in the class of children's bikes, the expense of a patriarch is saved and the efficiency of convenient operation is also provided.