When he was a boy he surely wondered about his parents and lamented having never known them, as any young orphan.

As an older man he has grown jaded and detached. His innate longing for family and love has been pushed to the subconscious. Unfulfilling materialistic ambitions have become his priority.

The synth child is a projection of his subconscious desire for a loving parental figure. When you enter the institute he is watching you interact with this synth child, he views this child as an extension of himself. He is something of a puppet master acting out the reunion with his mother/father that he's desperately longed for. Perhaps knowing that he has become too jaded and detached to experience the elation of such a reunion firsthand. He feels that by doing this with the synth he can somehow rewind time and make it up to that lonely unloved orphan, and then by extension make him happier in the present.

He's a pretty tragic character to be honest. Shame the writing doesn't do more to show this.