When lifting a stone, you first need the requisite mobility to pull yourself into a deep squat while having your hands on a fixed object. There are two places you can optimally stabilize your spine and trunk: one is while standing, and the other is in the bottom of a deep squat with an upright torso. (It can be done in other positions, but it is not nearly as effective.)
This is exactly what children do when trying to lift a heavy object. They will first explore the best way to lift the object in the deep squat and figure out how to grip it. If they feel comfortable, they will set spinal position and then come up into the hinge (deadlift position) to lift the object. If they cannot get a good grip, they will not pick it up. This will quickly expose any holes in your breathing and bracing strategies and your ability to effectively stabilize your trunk.