Ultimately, for me, family life is about sailing the ship together and sharing the experiences; commensurate with the age of ones children, of course. I think mutual catharsis, although the initial revelation is so emotive and potentially stressful, can begin immediately with everyone concerned, as you say. The children may not quite grasp at the time the full picture but I think later, as adults, they will appreciate the memories of shared catharsis instead feeling bereft of the truth. As an adult, I missed this opportunity; I'm sure many bereaved children, beyond a certain age, will feel the same way later if denied.
Yes, that's fine, but very hard if you've only got days to live when told it's terminal.