Off-topic, but:
> My kids have a photographic memory
How do you know it is photographic memory? More than one of your kids have it? Do you know why or what may have contributed to its development?
> Of each of these special pieces
I didn't see him making any generalized claim. I recall the things I'm really into better than I do things I'm not, which is all I think he was saying about his kids. (My four year old remembers facts about volcanos - including the name of the scientist who made the claim - waaay better than he does where he left his shoes, so it tracks for me!)
> My kids have a photographic memory of each of those special pieces and which set they came from.
Read the whole sentence- this is clearly an informal use of 'photographic memory' to indicate that his kids are really into Lego and keep track of details in the way only kids can.