A steering control coupling structure used in a children's wagon having a wheel assembly and a towing bar is disclosed to include a linking bracket affixed to the wheel axle of the wheel assembly, a first adapter affixed to a carriage and pivoted with the carriage to the linking bracket by a pivot device, the first adapter having a circular coupling hole and two 135° sector guide holes at two sides of the circular coupling hole, and a second adapter, which is affixed to the linking bracket around the pivot device and has a circular coupling block coupled to the circular hole of the first adapter and two 45° sector guide blocks respectively inserted into the 135° sector guide holes for forcing the second adapter to bias against the first adapter when the towing bar is biased to force the wheel assembly to change the steering direction.