Well, besides having similar (tho' not exact) facial features, I think both Alexei and Phillip Alford had that little-boy-turning-into-young-man look. When we think of Alexei during his final years, he is about the same age as was Alford at the time that To Kill A Mockingbird was filmed. And there is something very universal about boys at that age, having left childhood behind and being on the brink of manhood.
When, in his later years, Gregory Peck appeared in his "one man show," Phillip Alford attended on at least one occasion and was introduced to other audience members. Of course Alford is now a middle-aged man.
Just for the record I'll mention that I find To Kill a Mockingbird one of the best films ever made. Not only does it faithfully represent the story and ideas set down by author Harper Lee, but it is outstanding in every aspect of filmmaking. (The opening credits alone, shown while the haunting theme plays and the camera pans over items Jem and Scout have hidden away in the tree *, always brings me to tears.) And there are very few films that so beautifully capture the importance of respecting people, whatever their age, race, gender, or capability.
* Which, of course, reminds many of us about Alexei and his habit of collecting nails, string, etc.
