I agree that there may be valid reasons not to have photos from his childhood; fire, flood damage, loss in a move...there are lots of reasons why you might not have a lot of photos from 50 years ago. And before the digital age, when a photo was gone, it was gone. When I got married 20 years ago, I remember asking the wedding photographer how long he would keep the negatives on file, just in case.
I hope this is the missing case, because it would lovely for the family to have some answers while there's still time. But something about this just seems off to me. Several articles mention that the elder Damman has tried to call the man twice, to no avail. That sets off my hinky meter right there. I think I remember in the Shannon Sherrill hoax case that the family could never get hold of the woman, that she would call them but they could never reach her if they tried to call back? (Maybe I'm remembering that incorrectly.) Also, one of the linked articles says that the man's alleged biological mother was incoherent and on morphine when she mumbled something that MAY have been, "You're not my biological son." Who knows what she said or meant? If he has family and resentment issues, she could have said any number of unintelligible things that he chose to interpret as something to validate his "never fitting in." Even if she did say that, she could have meant, "Your father was married once before, to your mother, but we never talk about that because she committed suicide/ran away with a traveling salesman/was committed to an institution," or "My sister gave birth to you as an unmarried teenager, but since we didn't talk about those things in the 50s, you were given to the married daughter to raise as her own."
It is weird that the daughter and stroller were found, but he wasn't. My thought is that whoever snatched the children started to worry that they weren't getting away fast enough--too suspicious to start running down the street, but they were getting worried that the mom might come out and raise the alarm. So they didn't want to waste time unstrapping the girl from the stroller, so they just abandoned the stroller and ran off with the boy. Easier to hop in a waiting car with one child, too, instead of wrestling a stroller into the car. One of the articles said that there were several strollers lined up outside of the store; if one stroller is obviously missing, that's going to be the first thing that catches your eye, since a stroller (esp. the 1950s ones) is so large. Easy to scan the street and see that someone has your stroller; not as easy to tell from a distance that someone walking in the opposite direction has your child in their arms.