You can place a collection inside another collection, but this doesn’t parent anything in the 3d view.
But what you may want to do to move all objects together in the 3d view,
parent the front wheels to the front axle, the front axle to the front metal hardware, then the front metal hardware to the board, and do the same with the rear.
the only objects parented to the board will be the front and rear hardware.
Hope this makes sense!
