Is there a point in our life when ALL the atoms from our childhood's body get replaced?
Is there a point in our life when ALL the atoms from our childhood's body gets replaced?


No. There is no point where ALL atoms have been replaced. 

This has been shown by tracing distinct carbon isotopes in DNA [which reflect upon atmospheric 14C at the year of their generation (which reflect the extent of human atom bomb testing)]; Bergmann et al. 2009, Science: Evidence for Cardiomyocyte Renewal in Humans.



for your other questions:


  Is that fact widely accepted by the scientific community?


The phrasing of Richard Dawkins, which you also list, uses "more similar" (rather than the absolute ALL). These words provide quite an accurate approximation to express that  most building blocks of cells undergo a constant renewal. The choice of words of Grand seems a bit unlucky, if read out of context.


  Are the processes that repair DNA damage operating only in damaged areas?


As a first approximation: yes. For instance the image below shows the localized detection of H2A.X histones upon damage at the DNA (red: H2A.X staining -> much stronger in treated cells which have high level of damage; blue: DNA staining)




  Or do they constantly "repair" also healthy areas leading to the constant replacement of the atoms 


As one approximation this would be true, e.g.: proteostasis  (a process whose failure contributes to aging).


  that constitute the DNA?


Note that DNA molecules are vastly outnumbered by other molecules in a cell.

DNA is quite static (see above publication), although individual parts could possibly be repaired (see above image on H2A.X); 

Also there might be a selective retainment of more "healthy" DNA strands with less mutations (the immortal strand hypothesis).