The BFG isn't any standard giant that is bone-crunching. He is far too fine and jumbly. It's blessed for Sophie that he is. Had she been transported off at the middle of the night at the Bloodbottler, or any of the other giants--as opposed to the BFG--she'd have soon become morning meal. She decides she must stop them once and for everybody, when Sophie finds that the giants are flush-bunking off into swollomp a few small chiddlers. And the BFG is going to help her!