At this point in the game you are the hunter and are following the bird beyond the barricade and across the bridge. Well, after you complete all that and return with the boy, the boy is unable to go across the bridge. When you try to do so he simply sinks below the bridge and does not make it across. I've tried rebooting the game which made no difference.

Edit: I just verified the cache on Steam. Rebooted game and things worked normally.

Either way, FYI for the developers and any players that may experience this for themselves.