No one switched anyone. Mark identified himself in TWO sets of images of two little boys on his webpage. One image was tinted, one posted later, in black and white. The boys on the left and right are the child he identified as himself.
The boy in the centre is the recent image assumed to be Mark, although the image on the book cover, which seems to have been released prematurely (there is no book) does not identify the children.
So what you are looking at is two images of the child Mark claims is himself, and the centre image claimed to be Mark as the result of an unidentified image on the cover of a book which has not been released. I would recomment not jumping to conclusions.
The problem would appear to be, that if one of these little ones grew up to be zero, and the other one should happen to be Mark, you've lost your 'David'
And I hate to break it to you, but that might suggest the darker of the two childen was born in 1961, not all that long before the little tiger on the left. Have fun!
As if you don’t remember bringing those pictures on Mark’s site to my attention years ago in the wee hours one night and starting all this about the light boy being Barry.
There is no indication is these boys are anything more or less than who they were originally identified as: David and Mark.