A lot of people do not parent to geometry at all and it is imo usually the better way to go.
You can build a rig out of empties and then parent the geometry to these empties.
In this case you would have on emptyA for the leg and emptyB and emptyC for the wheels.
You would parent emptyB and emptyC to emptyA and then parent the leg to emptyA, wheel1 to emptyB and wheel2 to emptyC.
Then you would only animate the empties.
You would also not parent emptyA to the robots hip but instead create another empty, parent the leg empties to the hip and then parent the hip geometry to the hip.
This way you keep geometry and animation objects separate and things like the geomtries object origins don’t matter. You can also easily exchange the geometry for other models if needed and you don’t get problems in cases where you might need to scale the geometry.
Parenting stuff to geometry is almost never a good idea.
If it is a more complex rig it probably makes sense to use an armature.