The succession doesn't work like that, BATCO. Although you have to go back a while for the example (at least in terms of the monarch; the principles apply (with minor variations) to hereditary peers as well) George II outlived his son Frederick by 9 years; upon Geo II's death, Frederick's son became George III. Going even further back, Richard II was another instance of a grandson succeeding. Were Charles to predecease HMQ, the Duke of Cambridge would become heir apparent.
Only if Charles were to become king and then abdicate might the question about his children's place in the line of succession arise, since he might, in theory - like Edward VIII - be called upon to renounce the right of his descendants to the throne. This would be highly unlikely, though, since in Edward's case, he was childless, but had 'form'... The concern was that Mrs Simpson would leave him, that he'd marry someone in due course and have a child with her, whereupon that child would have had a claim to the throne. The renunciation of descendants' rights to the throne solved that possible problem.
In Charles's case, the line of succession is clear, and it would be inconceivable that the instrument of abdication would make any renunciation of William or George's position in the line.
Last edited by Archimedes; 4th Feb 2016 at 13:00.