...the problem is that Charles and Camilla are already at retirement age. They may feel the need to slow down a bit as well. Charles has been performing royal duties since he was a teenager. So I think it is expected that his children and their wives, who are themselves nearing middle-age, would become more involved in public duties.
SenecaFalls
Charles and Camilla are also a very Marmite pair - the RF can only present itself as 'relevant' if its leading members are popular, so I would expect Charles + Camilla, William and Kate, and Harry and Meghan to work as a team rather than pinning the future of the monarchy on C+C alone, which would be quite a risky bet.
I would say the children might also find themselves pressed into service unofficially - releases of photos of everyday life and milestones, meetings with world leaders (as with the Obamas and little George in his dressing gown), children included on trips abroad.