Originally Posted by
soyabean
The HCW-18 is used for a lot of one-piece cranks, virtually all kids' bikes.
But that is not the lock nut. If the OP was trying to move that while the lock nut was tight, I'm thinking they probably didn't budge it unless there was a lot of slack or play in the bearings.
On my one piece cranks, once the lock nut was loosened that part, the adjustment cone, could be moved with my fingers. Maybe sometimes needing a initial prod with the point of something. Punch, screwdriver and etc.